Quick answer
To deduce is to reach a conclusion by reasoning from evidence — Holmes deduces the answer. To deduct is to subtract an amount — deduct tax from a salary. Both come from the same Latin root meaning to lead away, and English split them for reasoning and arithmetic.
The core difference
One reasons; the other subtracts.
- deduce — conclude by reasoning: deduce the cause from the evidence.
- deduct — subtract: deduct expenses.
The nouns are the trap
Both give deduction, which does double duty: a logical deduction is a conclusion, and a tax deduction is a subtraction. Context always separates them, but it is why the verbs get confused — the noun offers no clue.
Deduction versus induction
In logic, deduction reasons from general premises to a specific conclusion; induction generalises from specific observations. Holmes, famously, mostly does the second while calling it the first.
Frequently asked questions
Which one means to subtract?
Deduct. To deduce is to conclude by reasoning.
Why do both give "deduction"?
They share a Latin root, and the noun covers both a logical conclusion and an arithmetical subtraction.
What is the difference between deduction and induction?
Deduction reasons from general premises to a specific conclusion; induction generalises from specific observations.
