physics

Mental substance

Mental substance is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mental substance rather than just read about it. In short: Mental substance, according to the idea held by dualists and idealists, is a non-physical substance of which minds are composed. This substance is often referred to as consciousness.

Key takeaways

Mental substance belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mental substance to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mental substance from memory before moving on to harder problems.

Reference excerpt

Mental substance, according to the idea held by dualists and idealists, is a non-physical substance of which minds are composed. This substance is often referred to as consciousness. This is opposed to the view of materialists, who hold that what we normally think of as mental substance is ultimately physical matter (i.e., brains). René Descartes, who was most famous for the assertion "I think therefore I am", played a major role in developing the mind–body problem. He describes his theory of mental substance (which he calls res cogitans distinguishing it from the res extensa) in the Second Meditation (II.8) and in Principia Philosophiae (2.002). He used a more precise definition of the word "substance" than is currently popular: that a substance is something which can exist without the existence of any other substance. For many philosophers, this word or the phrase "mental substance" has a special meaning. Descartes sought a foundation of knowledge that could not be doubted. He employed a method of radical doubt, questioning all beliefs that could possibly be uncertain. However, Descartes realized that the very act of doubting presupposed a thinking subject. If he was doubting, then he must be thinking; and if he was thinking, then he must exist as a thinking being. This insight led to his famous conclusion cogito, ergo sum ("I think, therefore I am").

History According to Descartes, God first created eternal truths and then the world from nothing, governing it with His divine providence. He took special care of human creatures, placing innate ideas in their thought, starting with the ideas of perfection and infinity. Gottfried Leibniz, belonging to the generation immediately after Descartes, held the position that the mental world was built up of monads, mental objects that are not part of the physical world (see Monadology). The distinction between res cogitans and res extensa was taken up in Spinoza's Ethics, written between 1661 and 1675, according to which Thought and Extension are two infinite attributes of the one divine Substance. Soul and body are in turn two finite modes of Thought and Extension.

See also Dualism (philosophy of mind) Monadology Monism Pluralism (philosophy of mind) Johannes Jacobus Poortman

References

Worked examples

Example 1 — a first encounter with Mental substance

Start with the simplest possible case. Write down what Mental substance claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mental substance before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mental substance ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mental substance

In research: Mental substance appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mental substance in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mental substance is common in secondary-school and first-year university syllabi. It links to neighbouring topics Concepts in metaphysics, Consciousness, Dualism (philosophy of mind), so understanding it makes those chapters shorter.
In everyday life: Look for Mental substance outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mental substance in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mental substance means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mental substance out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mental substance in simple terms?

Mental substance, according to the idea held by dualists and idealists, is a non-physical substance of which minds are composed. This substance is often referred to as consciousness.

Why does Mental substance matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mental substance?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mental substance.