Who invented collinear points?

Answer 1

It is meaningless to ask who "invented" collinear points, as they are simply accepted as an intuitive concept by the earliest mathematicians. The concept of a straight line passing through two points is postulated by Euclid of Alexandria in the beginning of his Elements, written about 300 B.C., but Euclid's books are, to a large extent, a compilation of the work of earlier mathematicians, so the concept obviously does not originate with Euclid. In particular, many of the proofs in books I and II of Euclid's Elements can be attributed to Pythagoras of Samos, so the concepts probably go back to before 500 B.C. The notion of a line and the points upon it are intuitive to human understanding; rope can be thought of as a physical analogue to an abstract line, making the concept immediately familiar to anyone. Euclid and Pythagoras probably felt no need to formally define the concept of a line, as the analogy was obvious. There is evidence that humans have been making cords and rope for over 28,000 years.