deduction

American  

[dih-duhk-shuhn] / dɪˈdʌk ʃən /

noun

1. the act or process of deducting; subtraction.

2. something that is or may be deducted.

   She took deductions for a home office and other business expenses from her taxes.

3. the act or process of deducing.

4. something that is deduced.

   His astute deduction was worthy of Sherlock Holmes.

5. Logic.

   1. a process of reasoning in which a conclusion follows necessarily from the premises presented, so that the conclusion cannot be false if the premises are true.

   2. a conclusion reached by this process.

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deduction British  

/ dɪˈdʌkʃən /

noun

1. the act or process of deducting or subtracting

2. something, esp a sum of money, that is or may be deducted

3. 1. the process of reasoning typical of mathematics and logic, whose conclusions follow necessarily from their premises

   2. an argument of this type

   3. the conclusion of such an argument

4. logic

   1. a systematic method of deriving conclusions that cannot be false when the premises are true, esp one amenable to formalization and study by the science of logic

   2. an argument of this type Compare induction

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deduction Scientific  

/ dĭ-dŭk′shən /

1. The process of reasoning from the general to the specific, in which a conclusion follows necessarily from the premises.

2. A conclusion reached by this process.

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deduction ¹ Cultural  

1. A process of reasoning that moves from the general to the specific. (Compare induction.)

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deduction ² Cultural  

1. A cost or expense subtracted from revenue, usually for tax purposes.

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Usage

The logical processes known as deduction and induction work in opposite ways. In deduction general principles are applied to specific instances. Thus, using a mathematical formula to figure the volume of air that can be contained in a gymnasium is applying deduction. Similarly, applying a law of physics to predict the outcome of an experiment is reasoning by deduction. By contrast, induction makes generalizations based on a number of specific instances. The observation of hundreds of examples in which a certain chemical kills plants might prompt the inductive conclusion that the chemical is toxic to all plants. Inductive generalizations are often revised as more examples are studied and more facts are known. If certain plants that have not been tested turn out to be unaffected by the chemical, the conclusion about the chemical's toxicity must be revised or restricted. In this way, an inductive generalization is much like a hypothesis.

Other Word Forms

• nondeduction noun
• prededuction noun

Etymology

Origin of deduction

First recorded in 1400–50; late Middle English deduccioun, from Anglo-French, from Latin dēductiōn-, stem of dēductiō “a leading away”; deduct, -ion

Example Sentences

You want to itemize this year when you took the standard deduction last year?

From MarketWatch • Mar. 23, 2026

The notional interest deduction saved Thermo Fisher nearly $1.2 billion in 2025.

From The Wall Street Journal • Mar. 20, 2026

That’s because, in addition to being voluntary, as Kleinbard noted, it’s uncapped — unlike, say the deduction of mortgage interest.

From Los Angeles Times • Mar. 19, 2026

This permanent universal charitable deduction will affect 90% of all U.S. households.

From Barron's • Mar. 17, 2026

This sickening deduction changed the way Ellsberg saw the Vietnam War.

From "Most Dangerous: Daniel Ellsberg and the Secret History of the Vietnam War" by Steve Sheinkin

Related Words

• abatement
• allowance
• credit
• discount
• rebate
• reduction
• tax write-off
• write-off