Aristotle (Ancient Greek: Ἀριστοτέλης, romanized: Aristotélēs; 384–322 BC) was an ancient Greek philosopher and polymath. His writings span the natural sciences, philosophy, linguistics, economics, politics, psychology, and the arts. As the founder of the Peripatetic school of philosophy in the Lyceum in Athens, he began the wider Aristotelian tradition that followed, which set the groundwork for the development of modern science. Little is known about Aristotle's life. He was born in the city of Stagira in Chalkidiki (northern Greece) during the Classical period. His father, Nicomachus, died when Aristotle was a child, and he was brought up by a guardian. At around eighteen years old, he joined Plato's Academy in Athens and remained there until the age of thirty seven (c. 347 BC). Shortly after Plato died, Aristotle left Athens and, at the request of Philip II of Macedon, tutored his son Alexander the Great beginning in 343 BC. He established a library in the Lyceum, which helped him to produce many of his hundreds of books on papyrus scrolls. Though Aristotle wrote many treatises and dialogues for publication, only around a third of his original output has survived, none of it intended for publication. Aristotle provided a complex synthesis of the various philosophies existing prior to him. His teachings and methods of inquiry have had a significant impact across the world, and remain a subject of contemporary philosophical discussion. Aristotle's views profoundly shaped medieval scholarship. The influence of his physical science extended from late antiquity and the Early Middle Ages into the Renaissance, and was not replaced systematically until the Enlightenment and theories such as classical mechanics were developed. He influenced Judeo-Islamic philosophies during the Middle Ages, as well as Christian theology, especially the Neoplatonism of the Early Church and the scholastic tradition of the Catholic Church. Aristotle was revered among medieval Muslim scholars as "The First Teacher", and among medieval Christians like Thomas Aquinas as simply "The Philosopher". He has been referred to as the first scientist. His works contain the earliest known systematic study of logic, and were studied by medieval scholars such as Peter Abelard and Jean Buridan. His influence on logic continued well into the 19th century. In addition, his ethics, although always influential, has gained renewed interest with the modern advent of virtue ethics.
Life In general, the details of Aristotle's life are not well-established. The biographies written in ancient times are often speculative and historians only agree on a few salient points. Aristotle was born in 384 BC in Stagira, Chalcidice, about 55 km (34 miles) east of modern-day Thessaloniki. He was the son of Nicomachus, the personal physician of King Amyntas of Macedon, and Phaestis, a woman with origins from Chalcis, Euboea. Nicomachus was said to have belonged to the medical guild of Asclepiadae and was likely responsible for Aristotle's early interest in biology and medicine. Ancient tradition held that Aristotle's family descended from the legendary physician Asclepius and his son Machaon. Both of Aristotle's parents died when he was still at a young age and Proxenus of Atarneus became his guardian. Although little information about Aristotle's childhood has survived, he probably spent some time in the Macedonian capital Pella, making his first connections with the Macedonian monarchy.
At the age of seventeen or eighteen, Aristotle moved to Athens to continue his education at Plato's Academy. He became distinguished as a researcher and lecturer, earning for himself the nickname "mind of the school" by his tutor Plato. In Athens, he probably experienced the Eleusinian Mysteries as he wrote when describing the sights one viewed at the Mysteries, "to experience is to learn" (παθεĩν μαθεĩν). Aristotle remained in Athens for nearly twenty years before leaving in 348/47 BC after Plato's death. The traditional story about his departure records that he was disappointed with the academy's direction after control passed to Plato's nephew Speusippus, although it is possible that the anti-Macedonian sentiments in Athens could have also influenced his decision. Aristotle left with Xenocrates to Assos in Asia Minor, where he was invited by his former fellow student Hermias of Atarneus; he stayed there for a few years, leaving around the time of Hermias' death. While at Assos, Aristotle and his colleague Theophrastus did extensive research in botany and marine biology, which they later continued at the near-by island of Lesbos. During this time, Aristotle married Pythias, Hermias's adoptive daughter and niece, and had a daughter whom they also named Pythias.
In 343/42 BC, Aristotle was invited to Pella by Philip II of Macedon to become the tutor to his thirteen-year-old son Alexander; a choice perhaps influenced by the relationship of Aristotle's family with the Macedonian dynasty. Aristotle taught Alexander at the private school of Mieza, in the gardens of the Nymphs, the royal estate near Pella. Alexander's education probably included a number of subjects, such as ethics and politics, as well as standard literary texts, like Euripides and Homer. It is likely that during Aristotle's time in the Macedonian court, other prominent nobles, like Ptolemy and Cassander, would have occasionally attended his lectures. Aristotle encouraged Alexander toward eastern conquest, and his own attitude towards Persia was strongly ethnocentric. In one famous example, he counsels Alexander to be "a leader to the Greeks and a despot to the barbarians". Alexander's education under the guardianship of Aristotle likely lasted for only a few years, as at around the age of sixteen he returned to Pella and was appointed regent of Macedon by his father Philip. During this time, Aristotle gifted Alexander an annotated copy of the Iliad, which is said to have become one of Alexander's most prized possessions. Scholars speculate that two of Aristotle's now lost works, On kingship and On behalf of the Colonies, were composed by the philosopher for the young prince. Aristotle returned to Athens for the second and final time a year after Philip II's assassination in 336 BC. As a metic, Aristotle could not own property in Athens and thus rented a building known as the Lyceum (named after the sacred grove of Apollo Lykeios), in which he established his own school. The building included a gymnasium and a colonnade (peripatos), from which the school acquired the name Peripatetic. Aristotle conducted courses and research at the school for the next twelve years. He often lectured small groups of distinguished students and, along with some of them, such as Theophrastus, Eudemus, and Aristoxenus, Aristotle built a large library which included manuscripts, maps, and museum objects. While in Athens, his wife Pythias died and Aristotle became involved with Herpyllis of Stagira. They had a son whom Aristotle named after his father, Nicomachus. This period in Athens, between 335 and 323 BC, is when Aristotle is believed to have composed many of his philosophical works. He wrote many dialogues, of which only fragments have survived. Those works that have survived are in treatise form and were not, for the most part, intended for widespread publication; they are generally thought to be lecture aids for his students. His most important treatises include Physics, Metaphysics, Nicomachean Ethics, Politics, On the Soul and Poetics. Aristotle studied and made significant contributions to "logic, metaphysics, mathematics, physics, biology, botany, ethics, politics, agriculture, medicine, dance, and theatre."
While Alexander deeply admired Aristotle, near the end of his life, the two men became estranged having diverging opinions over issues, like the optimal administration of city-states, the treatment of conquered populations, such as the Persians, and philosophical questions, like the definition of braveness. A widespread speculation in antiquity suggested that Aristotle played a role in Alexander's death, but the only evidence of this is an unlikely claim made some six years after the death. Following Alexander's death, anti-Macedonian sentiment in Athens was rekindled. In 322 BC, Demophilus and Eurymedon the Hierophant reportedly denounced Aristotle for impiety, prompting him to flee to his mother's family estate in Chalcis, Euboea, at which occasion he was said to have stated "I will not allow the Athenians to sin twice against philosophy" – a reference to Athens's trial and execution of Socrates. He died in Chalcis, Euboea of natural causes later that same year, having named his student Antipater as his chief executor and left a will in which he asked to be buried next to his wife. Aristotle left his works to Theophrastus, his successor as the head of the Lyceum, who in turn passed them down to Neleus of Scepsis in Asia Minor. There, the papers remained hidden for protection until they were purchased by the collector Apellicon. In the meantime, many copies of Aristotle's major works had already begun to circulate and be used in the Lyceum of Athens, Alexandria, and later in Rome.
Theoretical philosophy
Logic
With the Prior Analytics, Aristotle is credited with the earliest systematic study of logic, and his conception of it was the dominant form of Western logic until 19th-century advances in mathematical logic. Kant even stated in the Critique of Pure Reason that with Aristotle, logic reached its completion.
Organon
Most of Aristotle's work is probably not in its original form, because it was most likely edited by students and later lecturers. The logical works of Aristotle were compiled into a set of six books called the Organon around 40 BC by Andronicus of Rhodes or others among his followers. The books are:
Categories On Interpretation Prior Analytics Posterior Analytics Topics On Sophistical Refutations The order of the books (or the teachings from which they are composed) is not certain, but this list was derived from analysis of Aristotle's writings. It goes from the basics, the analysis of simple terms in the Categories, the analysis of propositions and their elementary relations in On Interpretation, to the study of more complex forms, namely, syllogisms and demonstration (in the Analytics) and dialectics (in the Topics and Sophistical Refutations). The first three treatises form the core of the logical theory stricto sensu: the grammar of the language of logic and the correct rules of reasoning. The Rhetoric is not conventionally included, but it states that it relies on the Topics.
Syllogism
What is today called Aristotelian logic with its types of syllogism (methods of logical argument), Aristotle himself would have labelled "analytics". The term "logic" he reserved to mean dialectics.
Demonstration Aristotle's Posterior Analytics contains his account of demonstration, or demonstrative knowledge, what would today be considered the study of epistemology rather than logic, but which for Aristotle is deeply connected with his account of syllogism. For Aristotle, knowledge is that which is necessarily the case, along with the study of causes.
Metaphysics
The word "metaphysics" comes from the title of a collection of works by Aristotle bearing that title. However, Aristotle did not use that term himself, which is due to a later compiler, but instead called it "first philosophy" or theology. He distinguished this as "the study of being qua being" which, as opposed to other studies of being, such as mathematics and natural science, studies that which is eternal, unchanging, and immaterial. He wrote in his Metaphysics (1026a16):
If there were no other independent things besides the composite natural ones, the study of nature would be the primary kind of knowledge; but if there is some motionless independent thing, the knowledge of this precedes it and is first philosophy, and it is universal in just this way, because it is first. And it belongs to this sort of philosophy to study being as being, both what it is and what belongs to it just by virtue of being.
Substance
Aristotle examines the concepts of substance (ousia) and essence (to ti ên einai, "the what it was to be") in his Metaphysics (Book VII), and he concludes that a particular substance is a combination of both matter and form, a philosophical theory called hylomorphism. In Book VIII, he distinguishes the matter of the substance as the substratum, or the stuff of which it is composed. For example, the matter of a house is the bricks, stones, timbers, etc., or whatever constitutes the potential house, while the form of the substance is the actual house, namely 'covering for bodies and chattels' or any other differentia that let us define something as a house. The formula that gives the components is the account of the matter, and the formula that gives the differentia is the account of the form.
Moderate realism
Like his teacher Plato, Aristotle's philosophy aims at the universal. Aristotle's ontology has the universal (katholou) exist in a lesser sense than particulars (kath' hekaston), things in the world, whereas for Plato the universal is a realer, separately existing form which particular things merely imitate. For Aristotle, universals still exist, but are only encountered when "instantiated" in a particular substance. In addition, Aristotle disagreed with Plato about the location of universals. Where Plato spoke of the forms as existing separately from the things that participate in them, Aristotle maintained that universals are multiply located. So, according to Aristotle, the form of apple exists within each apple, rather than in the world of the forms.
Potentiality and actuality Concerning the nature of change (kinesis) and its causes, as he outlines in his Physics and On Generation and Corruption (319b–320a), he distinguishes coming-to-be (genesis, also translated as 'generation') from:
growth and diminution, which is change in quantity; locomotion, which is change in space; and alteration, which is change in quality.
Coming-to-be is a change where the substrate of the thing that has undergone the change has itself changed. In that particular change he introduces the concept of potentiality (dynamis) and actuality (entelecheia) in association with the matter and the form. Referring to potentiality, this is what a thing is capable of doing or being acted upon if the conditions are right and it is not prevented by something else. For example, the seed of a plant in the soil is potentially (dynamei) a plant, and if it is not prevented by something, it will become a plant. Potentially, beings can either 'act' (poiein) or 'be acted upon' (paschein), which can be either innate or learned. For example, the eyes possess the potentiality of sight (innate – being acted upon), while the capability of playing the flute can be possessed by learning (exercise – acting). Actuality is the fulfilment of the end of the potentiality. Because the end (telos) is the principle of every change, and potentiality exists for the sake of the end, actuality, accordingly, is the end. Referring then to the previous example, it can be said that an actuality is when a plant does one of the activities that plants do.
For that for the sake of which (to hou heneka) a thing is, is its principle, and the becoming is for the sake of the end; and the actuality is the end, and it is for the sake of this that the potentiality is acquired. For animals do not see in order that they may have sight, but they have sight that they may see. In summary, the matter used to make a house has potentiality to be a house and both the activity of building and the form of the final house are actualities, which is also a final cause or end. Then Aristotle proceeds and concludes that the actuality is prior to potentiality in formula, in time and in substantiality. With this definition of the particular substance (i.e., matter and form), Aristotle tries to solve the problem of the unity of the beings, for example, "what is it that makes a man one"? Since, according to Plato there are two Ideas: animal and biped, how then is man a unity? However, according to Aristotle, the potential being (matter) and the actual one (form) are one and the same.
Natural philosophy Aristotle's "natural philosophy" spans a wide range of natural phenomena including those now covered by physics, biology and other natural sciences. In Aristotle's terminology, "natural philosophy" is a branch of philosophy examining the phenomena of the natural world, and includes fields that would be regarded today as physics, biology and other natural sciences. Aristotle's work encompassed virtually all facets of intellectual inquiry. Aristotle makes philosophy in the broad sense coextensive with reasoning, which he also would describe as "science". However, his use of the term science carries a different meaning than that covered by the term "scientific method". For Aristotle, "all science (dianoia) is either practical, poetical or theoretical" (Metaphysics 1025b25). His practical science includes ethics and politics; his poetical science means the study of fine arts including poetry; his theoretical science covers physics, mathematics and metaphysics.
Physics
Five elements
In his On Generation and Corruption, Aristotle related each of the four elements proposed earlier by Empedocles, earth, water, air, and fire, to two of the four sensible qualities, hot, cold, wet, and dry. In the Empedoclean scheme, all matter was made of the four elements, in differing proportions. Aristotle's scheme added the heavenly aether, the divine substance of the heavenly spheres, stars and planets.
Motion
Aristotle describes two kinds of motion: "violent" or "unnatural motion", such as that of a thrown stone, in the Physics (254b10), and "natural motion", such as of a falling object, in On the Heavens (300a20). In violent motion, as soon as the agent stops causing it, the motion stops also: in other words, the natural state of an object is to be at rest, since Aristotle does not address friction. With this understanding, it can be observed that, as Aristotle stated, heavy objects (on the ground, say) require more force to make them move; and objects pushed with greater force move faster. This would imply the equation
F = m v {\displaystyle F=mv} , incorrect in modern physics. Natural motion depends on the element concerned: the aether naturally moves in a circle around the heavens, while the 4 Empedoclean elements move vertically up (like fire, as is observed) or down (like earth) towards their natural resting places.
In the Physics (215a25), Aristotle effectively states a quantitative law, that the speed, v, of a falling body is proportional (say, with constant c) to its weight, W, and inversely proportional to the density, ρ, of the fluid in which it is falling:
v = c W ρ {\displaystyle v=c{\frac {W}{\rho }}}
Aristotle implies that in a vacuum the speed of fall would become infinite, and concludes from this apparent absurdity that a vacuum is not possible. Opinions have varied on whether Aristotle intended to state quantitative laws. Henri Carteron held the "extreme view" that Aristotle's concept of force was basically qualitative, but other authors reject this. Archimedes corrected Aristotle's theory that bodies move towards their natural resting places; metal boats can float if they displace enough water; floating depends in Archimedes' scheme on the mass and volume of the object, not, as Aristotle thought, its elementary composition. Aristotle's writings on motion remained influential until the early modern period. John Philoponus (in late antiquity) and Galileo (in the early modern period) are said to have shown by experiment that Aristotle's claim that a heavier object falls faster than a lighter object is incorrect. A contrary opinion is given by Carlo Rovelli, who argues that Aristotle's physics of motion is correct within its domain of validity, that of objects in the Earth's gravitational field immersed in a fluid such as air. In this system, heavy bodies in steady fall indeed travel faster than light ones (whether friction is ignored, or not), and they do fall more slowly in a denser medium. Isaac Newton's "forced" motion corresponds to Aristotle's "violent" motion with its external agent, but Aristotle's assumption that the agent's effect stops immediately it stops acting (e.g., the ball leaves the thrower's hand) has awkward consequences: he has to suppose that surrounding fluid helps to push the ball along to make it continue to rise even though the hand is no longer acting on it, resulting in the Medieval theory of impetus.
Four causes
Aristotle distinguished between four different "causes"(Ancient Greek: αἰτία, aitia) or explanations for why an object exists or changes:
The material cause describes the material out of which something is composed. Thus the material cause of a wooden table is the wood it is made of. The formal cause is its form, i.e., the arrangement of that matter, the design of the table independent of the specific material it is made of. The efficient cause is "the primary source", the modern definition of "cause" as either the agent or agency of particular events or states of affairs. In the case of two dominoes, when the first is knocked over it causes the second to fall. In the case of an animal, this agency is a combination of how it develops from the egg, and how its body functions. The final cause (telos) is its purpose, the reason why it exists or is done, or function that something is supposed to serve. In the case of living things, it implies adaptation to a particular way of life.
Optics Aristotle was aware of Pythagorean optics. He used optics in his Meteorology, treating it as a science. He viewed optics as stating the laws of sight, thus combining what is now treated as physics and biology. The process of seeing involved the movement of a visible form from the thing seen through the air (or other medium) to the eye, where the form comes to rest. Aristotle does not analyse the nature of this movement; he does not anticipate geometrical optics.
Chance and spontaneity
According to Aristotle, spontaneity and chance are causes of some things, distinguishable from other types of cause such as simple necessity. Chance as an incidental cause lies in the realm of accidental things, "from what is spontaneous". There is also more a specific kind of chance, which Aristotle names "luck", that only applies to people's moral choices.
Astronomy
In astronomy, Aristotle refuted Democritus's claim that the Milky Way was made up of "those stars which are shaded by the earth from the sun's rays," pointing out partly correctly that if "the size of the sun is greater than that of the earth and the distance of the stars from the earth many times greater than that of the sun, then... the sun shines on all the stars and the earth screens none of them." He also wrote descriptions of comets, including the Great Comet of 371 BC.
Geology and natural sciences
Aristotle was one of the first people to record any geological observations. He stated that geological change was too slow to be observed in one person's lifetime. The geologist Charles Lyell noted that Aristotle described such change, including "lakes that had dried up" and "deserts that had become watered by rivers", giving as examples the growth of the Nile delta since the time of Homer, and "the upheaving of one of the Aeolian islands, previous to a volcanic eruption." Meteorologica lends its name to the modern study of meteorology, but its modern usage diverges from the content of Aristotle's ancient treatise on meteors. The ancient Greeks did use the term for a range of atmospheric phenomena, but also for earthquakes and volcanic eruptions. Aristotle proposed that the cause of earthquakes was a gas or vapour (anathymiaseis) that was trapped inside the earth and trying to escape, following other Greek authors Anaxagoras, Empedocles and Democritus. Aristotle also made many observations about the hydrologic cycle. For example, he made some of the earliest observations about desalination: he observed early – and correctly – that when seawater is heated, freshwater evaporates and that the oceans are then replenished by the cycle of rainfall and river runoff ("I have proved by experiment that salt water evaporated forms fresh and the vapour does not when it condenses condense into sea water again.")
Biology
Empirical research Aristotle was the first person to study biology systematically, and biology forms a large part of his writings. He spent two years observing and describing the zoology of Lesbos and the surrounding seas, including in particular the Pyrrha lagoon in the centre of Lesbos. His data in History of Animals, Generation of Animals, Movement of Animals, and Parts of Animals are from his own observations, statements by knowledgeable people such as beekeepers and fishermen, and accounts by travellers. His apparent emphasis on animals rather than plants is a historical accident: his works on botany have been lost, but two books on plants by his pupil Theophrastus have survived. Aristotle reports on sea life from observation on Lesbos and the catches of fishermen. He describes the catfish, electric ray, and frogfish, as well as cephalopods such as the octopus and paper nautilus. His description of the hectocotyl arm of cephalopods, used in sexual reproduction, was widely disbelieved until the 19th century. He gives accurate descriptions of the four-chambered stomachs of ruminants, and of the ovoviviparous embryological development of the hound shark. He notes that an animal's structure is well matched to function so the heron has a long neck, long legs, and a sharp spear-like beak, whereas ducks have short legs and webbed feet. Darwin, too, noted such differences, but unlike Aristotle used the data to come to the theory of evolution. Aristotle's writings can seem to imply evolution, but Aristotle saw mutations or hybridizations as rare accidents, distinct from natural causes. He was thus critical of Empedocles's theory of a "survival of the fittest" origin of living things and their organs, and ridiculed the idea that accidents could lead to orderly results. In modern terms, he nowhere says that different species can have a common ancestor, that one kind can change into another, or that kinds can become extinct.
Scientific style
Aristotle did not do experiments in the modern sense. He made observations, or at most investigative procedures like dissection. In Generation of Animals, he opens a fertilized hen's egg to see the embryo's heart beating inside. Instead, he systematically gathered data, discovering patterns common to whole groups of animals, and inferring possible causal explanations from these. This style is common in modern biology when large amounts of data become available in a new field, such as genomics. This sets out testable hypotheses and constructs a narrative explanation of what is observed. In this sense, Aristotle's biology is scientific.
From his data, Aristotle inferred rules relating the life-history features of live-bearing tetrapods (terrestrial placental mammals) that he studied. He correctly predicted that brood size decreases with body mass; that lifespan increases with gestation period and with body mass; and that fecundity decreases with lifespan.
Classification of living things
Aristotle distinguished about 500 animal species, arranging them in a nonreligious graded scale of perfection, with man at the top. The highest gave live birth to hot and wet creatures, the lowest laid cold, dry mineral-like eggs. He grouped what a zoologist would call vertebrates as "animals with blood", and invertebrates as "animals without blood". Those with blood were divided into live-bearing (mammals), and egg-laying (birds, reptiles, fish). Those without blood were insects, crustacea and hard-shelled molluscs. He recognised that animals did not exactly fit onto a scale, and noted exceptions, such as that sharks had a placenta. To a biologist, the explanation is convergent evolution. Philosophers of science have concluded that Aristotle was not interested in taxonomy, but zoologists think otherwise.
Psychology
Soul
Aristotle's psychology, in his treatise On the Soul (peri psychēs), posits three kinds of soul (psyches): the vegetative, sensitive, and rational. Humans have all three. The vegetative soul is concerned with growth and nourishment. The sensitive soul experiences sensations and movement. The uniquely human, rational soul receives forms of things and compares them using the nous (intellect) and logos (reason). For Aristotle, the soul is the form of a living being. Because all beings are composites of form and matter, the form of living beings is that which endows them with what is specific to living beings, e.g., the ability to initiate movement. In contrast to earlier philosophers, but in accordance with the Egyptians, he placed the rational soul in the heart. Aristotle distinguished sensation and thought, unlike previous philosophers except for Alcmaeon. In On the Soul, Aristotle criticizes Plato's theory of the soul and develops his own in response. Firstly he criticises Plato's Timaeus which holds the soul takes up space and can come into physical contact with bodies. 20th-century scholarship held that Aristotle had here misinterpreted Plato. Aristotle also argued that Plato's view of reincarnation entails that a soul and its body can be mis-matched; in principle, Aristotle alleges, any soul can go with any body, according to Plato's theory.
Memory According to Aristotle in On the Soul, memory is the ability to hold a perceived experience in the mind and to distinguish between the internal "appearance" and a past occurrence. A memory is a mental picture (phantasm) that can be recovered. An impression is left on a semi-fluid bodily organ that undergoes changes in order to make a memory. A memory occurs when stimuli such as sights or sounds are so complex that the nervous system cannot receive them all at once. These changes are the same as those involved in sensation, 'common sense', and thinking. Aristotle uses the term 'memory' for the actual retaining of an experience in the impression that develops from sensation, and for the intellectual anxiety that comes with the impression because it is formed at a particular time and processing specific contents. Memory is of the past, prediction is of the future, and sensation is of the present. Retrieval of impressions cannot be performed suddenly. A transitional channel is needed and located in past experiences, both for previous experience and present experience. Because Aristotle believed people perceive all kinds of sense perceptions as impressions, people continually weave together new impressions of experiences. To search for impressions, people search memory itself. Within memory, if an experience is offered instead of a specific memory, that person will reject this experience until they find what they are looking for. Recollection occurs when a retrieved experience naturally follows another. If the chain of "images" is needed, one memory stimulates the next. When people recall experiences, they stimulate certain previous experiences until they reach the one that is needed. Recollection is thus the self-directed activity of retrieving information stored in a memory impression. Only humans can remember impressions of intellectual activity, such as numbers and words. Animals that have perception of time can retrieve memories of their past observations. Remembering involves only perception of the things remembered and of the time passed.
Aristotle believed the chain of thought that achieves recollection of impressions was connected systematically in relationships such as similarity, contrast, and contiguity, described in his laws of association. Aristotle believed that past experiences are hidden within the mind. A force operates to awaken the hidden material to bring up the actual experience. Association is the power innate in a mental state, which operates upon the unexpressed remains of former experiences, allowing them to be recalled.
Dreams
Aristotle describes sleep in On Sleep and Wakefulness. It is a result of overuse of the senses or of digestion, and is vital to the body. While a person is asleep, the critical activities, which include thinking, sensing, recalling and remembering, do not function. Since a person cannot sense during sleep, they cannot have desire. However, the senses work during sleep, albeit differently. Dreams do not involve sensing a stimulus. Sensation is involved, but in an altered manner. Aristotle explains that when a person stares at a moving stimulus such as the waves in a body of water, and then looks away, the next thing they look at appears to have a wavelike motion. When a person perceives a stimulus and it is no longer the focus of their attention, it leaves an impression. When the body is awake, a person constantly encounters new stimuli and so the impressions of previous stimuli are ignored. However, during sleep the impressions made throughout the day are noticed, free of distractions. So, dreams result from these lasting impressions. Since impressions are all that are left, dreams do not resemble waking experience. During sleep, a person is in an altered state of mind, like a person who is overtaken by strong feelings. For example, a person who has a strong infatuation with someone may begin to think they see that person everywhere. Since a person sleeping is in a suggestible state and unable to make judgements, they become easily deceived by what appears in their dreams, like the infatuated person. This leads them to believe the dream is real, even when the dreams are absurd. In De Anima iii 3, Aristotle ascribes the ability to create, to store, and to recall images to the faculty of imagination, phantasia. One component of Aristotle's theory disagrees with previously held beliefs. He claimed that dreams are not foretelling and not sent by a divine being. Aristotle reasoned that instances in which dreams resemble future events are simply coincidences. Any sensory experience perceived while a person is asleep, such as actually hearing a door close, does not qualify as part of a dream. Images of dreams must be a result of lasting impressions of waking sensory experiences.
Practical philosophy Aristotle's practical philosophy covers areas such as ethics, politics, economics, and rhetoric.
Ethics
Aristotle was a virtue ethicist who considered ethics to be a practical rather than theoretical study, i.e., one aimed at becoming good and doing good rather than knowing for its own sake. He wrote several treatises on ethics, most notably including the Nicomachean Ethics. Aristotle taught that virtue has to do with the proper function (ergon) of a thing. An eye is only a good eye in so much as it can see because the proper function of an eye is sight. Aristotle reasoned that humans must have a function specific to humans, and that this function must be an activity of the psuchē (soul) in accordance with reason (logos). Aristotle identified such an optimum activity (the virtuous mean, between the accompanying vices of excess or deficiency) of the soul as the aim of all human deliberate action, eudaimonia, generally translated as "happiness" or sometimes "well-being". To have the potential of ever being happy in this way necessarily requires a good character (ēthikē aretē), often translated as moral or ethical virtue or excellence. Aristotle taught that to achieve a virtuous and potentially happy character requires a first stage of having the fortune to be habituated, not deliberately, but by teachers, and experience, leading to a later stage in which one consciously chooses to do the best things, becoming the phronimos or virtuous man. When the best people come to live life this way their practical wisdom (phronesis) and their intellect (nous) can develop with each other towards the highest possible human virtue, the wisdom of an accomplished theoretical or speculative thinker, or in other words, a philosopher.
Politics
In addition to his works on ethics, which address the individual, Aristotle addressed the city in his work titled Politics. Aristotle considered the city to be a natural community. Moreover, he considered the city to be prior in importance to the family, which in turn is prior to the individual, "for the whole must of necessity be prior to the part". He famously stated that "man is by nature a political animal" and argued that humanity's defining factor among others in the animal kingdom is its rationality. Aristotle conceived of politics as being like an organism rather than like a machine, and as a collection of parts, none of which can exist without the others. Aristotle's conception of the city is organic, and he is considered one of the first to conceive of the city in this manner.
The common modern understanding of a political community as a modern state is quite different from Aristotle's understanding. Although he was aware of the existence and potential of larger empires, the natural community according to Aristotle was the city (polis) which functions as a political "community" or "partnership" (koinōnia). The aim of the city is not just to avoid injustice or for economic stability, but rather to allow at least some citizens the possibility to live a good life, and to perform beautiful acts: "The political partnership must be regarded, therefore, as being for the sake of noble actions, not for the sake of living together." This is distinguished from modern approaches, beginning with social contract theory, according to which individuals leave the state of nature because of "fear of violent death" or its "inconveniences". In Protrepticus, the character 'Aristotle' states:
For we all agree that the most excellent man should rule, i.e., the supreme by nature, and that the law rules and alone is authoritative; but the law is a kind of intelligence, i.e., a discourse based on intelligence. And again, what standard do we have, what criterion of good things, that is more precise than the intelligent man? For all that this man will choose, if the choice is based on his knowledge, are good things and their contraries are bad. And since everybody chooses most of all what conforms to their own proper dispositions (a just man choosing to live justly, a man with bravery to live bravely, likewise a self-controlled man to live with self-control), it is clear that the intelligent man will choose most of all to be intelligent; for this is the function of that capacity. Hence it's evident that, according to the most authoritative judgment, intelligence is supreme among goods. As Plato's disciple Aristotle was rather critical concerning democracy and, following the outline of certain ideas from Plato's Statesman, he developed a coherent theory of integrating various forms of power into a so-called mixed state:
It is ... constitutional to take ... from oligarchy that offices are to be elected, and from democracy that this is not to be on a property-qualification. This then is the mode of the mixture; and the mark of a good mixture of democracy and oligarchy is when it is possible to speak of the same constitution as a democracy and as an oligarchy.
Economics
Aristotle made substantial contributions to economic thought, especially to thought in the Middle Ages. In Politics, Aristotle addresses the city, prope