Pronunciation: /dɪˈdʌk ʃən/ Explain
Deduction is a form of reasoning that uses
premises that are agreed upon to support a conclusion.
In mathematics, the premises are called
If the premises on which deduction is based are true, and if a deductive argument is
then the conclusion must be true. If the premises are all true and the deduction is valid,
then the argument is sound. If any of the premises are false, or
if the deduction is invalid, then the argument is unsound.
If any of the premises are false, then
the conclusion may or may not be true. Look at table 2. The first premise, 'All humans
are mammals,' is correct. The second premise, 'All mammals have toes,' is incorrect. Hoofed
animals such as horses do not have toes. Yet the conclusion, 'All humans have toes,' is
correct. The conclusion is true, but the argument is unsound.
|All men are mortal.||Premise
|Socrates is a man.||Premise
|Therefore Socrates is mortal.||Conclusion
|Table 1: Aristotle's example of deduction.|
|All humans are mammals.||Correct premise
|All mammals have toes.||Incorrect premise
|Therefore all humans have toes.||Conclusion
|Table 2: Example of unsound deduction.|
- Assumption: A premise that is assumed to be true without proof.
- Axiom: A mathematical statement that is taken to be true without proof.
- Deductive: Based on deduction - deductive reasoning.
- Hypothesis: A claim that is proposed to be true, but has not been proved.
- Conjecture: A claim that is consistent with known data and is believed to be true, but has not been proved.
- Postulate: A premise that is assumed to be true without proof.
- Premise: An axiom or previously proved theorem used to support a conclusion.
- Theorem: A claim that has already been proved.
- Jevons, Stanley W.. Logic. pp 12-14. www.archive.org. American Book Company. 189?. Last Accessed 8/6/2018. http://www.archive.org/stream/logicjevons00jevoiala#page/12/mode/1up/search/deductive. Buy the book
- Bain, Alexander. Logic, Part First, Deduction. www.archive.org. Longmans, Green, & Co.. 1879. Last Accessed 8/6/2018. http://www.archive.org/stream/logicbain00bainiala#page/n2/mode/1up. Buy the book
- O'Connor, J J and Robertson, E F. Aristotle. School of Mathematics and Statistics, University of St Andrews, Scotland. 3/12/2009. http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Aristotle.html.
Cite this article as:
McAdams, David E. Deduction. 8/27/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/d/deduction.html.
8/27/2018: Corrected spelling. (McAdams, David E.)
7/3/2018: Removed broken links, updated license, implemented new markup, implemented new Geogebra protocol. (McAdams, David E.)
1/22/2010: Added "References". (McAdams, David E.)
1/27/2009: Added second paragraph to description. Added example 2 (McAdams, David E.)
7/10/2008: Added conjecture to the list of related words. (McAdams, David E.)
4/14/2008: Initial version. (McAdams, David E.)