the.com/deduction

working backwards from truth until the only suspect left is certainty.

means A conclusion reached by reasoning from general premises to a logical certainty, or an amount subtracted from a total.

from From Latin 'deductio,' a leading down or drawing away, from 'deducere' — 'de-' (down, away) plus 'ducere' (to lead). The same 'ducere' that marches through 'conduct,' 'produce,' and 'duke.' So a deduction is, quite literally, a leading-away: pulling a smaller thing out of a larger one, whether that's a sum from your paycheck or a truth from a heap of facts.

Sherlock myth: Holmes mostly used induction, not deduction
Aristotle's toy: He formalized the syllogism over 2,300 years ago
Tax flavor: Same word means shrinking your taxable income
Logic's promise: True premises guarantee a true conclusion
No new facts: It only unpacks what premises already contain

for instance

sherlock holmes — fictional detective who solved crimes through logical deduction in 56 stories by arthur conan doyle starting 1887

dna fingerprinting — forensic technique using deductive matching of genetic profiles, first used to convict colin pitchfork in 1988

tax deduction — us irs deductions that reduce taxable income, with standard deduction of $13,850 for 2023