He rejected these traditional explanations about why things happened. Instead, he replaced them with rational explanations, based on experiments, astronomy, and scientific inquiry. He asked questions such as, “How can nature be described mathematically?” He tried to discover universal principles to explain the whole of Nature.
Therefore, he was one of the first to employ the scientific method as well as to delve into the nature of reality, and thus combine science with philosophy.
But this is just in the Western Tradition. The Buddha and Lao Tsu had established their ways of looking at the world at roughly the same time as Thales, so it is not accurate to say that he is the world’s first philosopher, without qualifying it with the word “Greek.” And since written records are not easily available from those times, we can only surmise that he was the first Greek philosopher, though there doubtless were other thinkers who did not reach his level of fame.