science

Necessity good

Necessity good 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 Necessity good rather than just read about it. In short: In economics, a necessity good or a necessary good is a type of normal good, and they are usually classified as an inferior good. Necessity goods are product(s) and services that consumers will buy regardless of the changes in their income levels, therefore making these products less sensitive to income change.

Key takeaways

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

Reference excerpt

In economics, a necessity good or a necessary good is a type of normal good, and they are usually classified as an inferior good. Necessity goods are product(s) and services that consumers will buy regardless of the changes in their income levels, therefore making these products less sensitive to income change. Necessity goods are goods or services which are indispensable to humans, such as food, water, or shelter. Necessity goods often do not have close substitute goods. As for any other normal good, an income rise will lead to a rise in demand, but the increase for a necessity good is less than proportional to the rise in income, so the proportion of expenditure on these goods falls as income rises. If income elasticity of demand is lower than unity, it is a necessity good. This observation for food, known as Engel's law, states that as income rises, the proportion of income spent on food falls, even if absolute expenditure on food rises. This makes the income elasticity of demand for food between zero and one. Some necessity goods are produced by a public utility or by state-owned monopolies. According to Investopedia, stocks of private companies producing necessity goods are known as defensive stocks. Defensive stocks are stocks that provide a constant dividend and stable earnings regardless of the state of the overall stock market. The opposite of a necessity good is a luxury good, which in economics is a "good or service whose consumption rises more than in proportion to rises in income."

See also Basic needs Income elasticity of demand Wealth (economics)

References

Illustrations

Worked examples

Example 1 — a first encounter with Necessity good

Start with the simplest possible case. Write down what Necessity good 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 Necessity good 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 Necessity good 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 Necessity good

In research: Necessity good 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 Necessity good 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: Necessity good is common in secondary-school and first-year university syllabi. It links to neighbouring topics Goods, Microeconomics stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Necessity good 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 Necessity good in 20 minutes

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

Frequently asked questions

What is Necessity good in simple terms?

Why does Necessity good 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 Necessity good?

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 Necessity good.