# The Most Influential

# People in History

## Thales of Miletus/THAY-leez /

###### c. 624–c. 545 B.C.E

###### Greek Mathematician, Astronomer, and Philosopher

###### Mathematics Ranking 10th of 46

###### Thales on a Greek stamp from 1994.

Thales is one of the earliest Greek mathematicians, is considered the first Greek philosopher, and was a remarkable astronomer. Thales is also considered the founder of geometry and therefore laid the groundwork for later Greek mathematicians, including Euclid and Archimedes. Using deductive reasoning, Thales used certain known relationships to deduce (find) new relationships called theorems. The introduction of proof by deductive reasoning by Thales was one of the most important steps in the development of human thought processes.(1)

##### A Deductive Proof

#####

Prove: Triangle ABC is congruent to triangle CDE, if AC = CE.

His mathematical achievements are difficult to assess, however, because of the ancient practice of crediting particular discoveries to men with a general reputation for wisdom.(2) Aristotle held that Thales was the founder of physical science. (3) No writings by Thales survive, and no contemporary sources exist, thus his achievements are difficult to assess. (4)

Footnotes:

(1) Alan Wise, Introductory Geometry – A Brief Course with Reasoning Skills (New York, 1990), p. 11.

(2) Encyclopedia Britannica, Micropaedia, Volume 11, 1993, 15th Edition, p. 670 (from “In geometry”).

(3) Judy Pearsall and Bill Trumbell (editors), The Oxford Encyclopedic English Dictionary (New York, 1996), p. 1493.

(4) Encyclopaedia Britannica, Micropaedia, Volume 11, 1993, 15th Edition, p. 670.