Less controversial than the position that Thales learnt Babylonian mathematics is the claim he was influenced by Egyptians. Pointedly Historian S. N. Bychkov holds that the idea that the base angles of an isosceles triangle are equal likely came from Egypt. This is because, when building a roof for a home - having a cross section be exactly an isosceles triangle isn't crucial (as it's the ridge of the roof that must fit precisely), in contrast a symmetric square pyramid cannot have errors in the base angles of the faces or they will not fit together tightly. Historian D.R. Dicks agrees that compared to the Greeks in the era of Thales, there was a more advanced state of mathematics among the Babylonians and especially the Egyptians - "both cultures knew the correct formulae for determining the areas and volumes of simple geometrical figures such as triangles, rectangles, trapezoids, etc.; the Egyptians could also calculate correctly the volume of the frustum of a pyramid with a square base (the Babylonians used an incorrect formula for this), and used a formula for the area of a circle...which gives a value for π of 3.1605--a good approximation." Dicks also agrees that this would have had an effect on Thales (whom the most ancient sources agree was interested in mathematics and astronomy) but he holds that tales of Thales' travels in these lands are pure myth.

The 1870 book Dictionary of Greek and Roman Biography and Mythology noted

Historian D.R. Dicks and other historians divide the ancient sources about Thales into those before 320 BC and those after that year (some such as Proclus writing in the 5th century C.E. and Simplicius of Cilicia in the 6th century C.E. writing nearly a millennium after his era). The first category includes Herodotus, Plato, Aristotle, Aristophanes, and Theophrastus among others. The second category includes Plautus, Aetius, Eusebius, Plutarch, Josephus, Iamblichus, Diogenes Laërtius, Theon of Smyrna, Apuleius, Clement of Alexandria, Pliny the Elder, and John Tzetzes among others.

Thales was probably born in the city of Miletus around the mid-620s BC. The ancient Writer Apollodorus of Athens writing during the 2nd century BC, thought Thales was born about the year 625 BC. Herodotus, writing in the fifth century BC, described Thales as "a Phoenician by remote descent". The later Historian Diogenes Laertius, in his Lives of the Philosophers, references Herodotus, Duris, and Democritus, who all agree "that Thales was the son of Examyas and Cleobulina, and belonged to the Thelidae who are Phoenicians." He then states that "Most Writers, however, represent him as a native of Miletus and of a distinguished family."

Aristotle laid out his own thinking about matter and form which may shed some light on the ideas of Thales, in Metaphysics 983 b6 8–11, 17–21. (The passage contains words that were later adopted by science with quite different meanings.)

This story indicates that he was familiar with the Egyptian seked, or seqed, the ratio of the run to the rise of a slope (cotangent). The seked is at the base of problems 56, 57, 58, 59 and 60 of the Rhind papyrus — an ancient Egyptian mathematical document.

Thales applied his method to objects that changed to become other objects, such as water into earth (or so he thought). Thales also applied his method to the act of change itself, approaching it through lodestone and amber (which, when electrified by rubbing together, also attracts). As for the ability of a mover to move something else without being changed itself, Thales saw a commonality between that and the power of a living thing to act. The lodestone and the amber must be alive, and if that were so, there could be no difference between the living and the dead. When asked why he didn’t die if there was no difference, he replied "because there is no difference."