Natural deduction is a branch of mathematical logic developed in Poland in the 1920s and 30s. It is meant to express inference rules closely related to the "natural" way of reasoning. However, it does not mean "how ordinary people think".
Spurred on by a series of seminars in Poland in 1926 by Łukasiewicz that advocated a more natural treatment of logic, Jaśkowski made the earliest attempts at defining a more natural deduction. In 1929 he first suggested in 1929 using a diagrammatic notation, and later updated his proposal in papers in 1934 and 1935.
- Jaśkowski, Stanaslaw 1934. On the rules of suppositions in formal logic.
- Jon Barwise and John Etchemendy, 2000. Language, proof and logic. CSLI (University of Chicago Press) and New York: Seven Bridges Press. A gentle introduction to first-order logic via natural deduction, by two first rate logicians.
- Clemente, Daniel, "Introduction to natural deduction."
- Pelletier, Jeff, "A history of natural deduction and elementary logic textbooks."