science

Fundamental psychological law

Fundamental psychological law is a science 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 Fundamental psychological law rather than just read about it. In short: In Keynesian macroeconomics, the Fundamental Psychological Law underlying the consumption function states that marginal propensity to consume (MPC) and marginal propensity to save (MPS) are greater than zero(0) but less than one(1) MPC+MPS = 1 e.g. Whenever national income rises by $1 part of this will be consumed and part of this will be saved References Keynes, J.

Key takeaways

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

Reference excerpt

In Keynesian macroeconomics, the Fundamental Psychological Law underlying the consumption function states that marginal propensity to consume (MPC) and marginal propensity to save (MPS) are greater than zero(0) but less than one(1) MPC+MPS = 1 e.g. Whenever national income rises by $1 part of this will be consumed and part of this will be saved

References Keynes, J. M. (1937), "The General Theory of Employment", Quarterly Journal of Economics, 51: 209–223, doi:10.2307/1882087. Albert Hahn, L (1949). The Economics of Illusion:Critical analysis of contemporary economic theory and policy. USA: Squier Publishing company. Murad, Anatol. What Keynes Means. USA. Hirai, Toshiaki (2008). Keynes Theoretical Development- from the tract to the General theory. Milton Park, Abingdon: Routledge.

Worked examples

Example 1 — a first encounter with Fundamental psychological law

Start with the simplest possible case. Write down what Fundamental psychological law claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Fundamental psychological law 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 Fundamental psychological law 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 Fundamental psychological law

In research: Fundamental psychological law appears in science 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 Fundamental psychological law 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: Fundamental psychological law is common in secondary-school and first-year university syllabi. It links to neighbouring topics Keynesian economics, Macroeconomics stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Fundamental psychological law 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 Fundamental psychological law in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Fundamental psychological law 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 Fundamental psychological law out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Fundamental psychological law in simple terms?

Why does Fundamental psychological law matter?

Because it connects several science 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 Fundamental psychological law?

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 Fundamental psychological law.