Juliet asked:

Compare and contrast Thales and Anaximander theory which one do you find more plausible.

Answer by Jürgen Lawrenz

We don’t actually know what their theories were. Most of what we know about them is conjecture, because none of their writings survive. In addition, a lot of the material written much later is highly untrustworthy. So this is a problem.

But from what we understand, Thales theorised about what we today would call an ‘ultimate substance’, or the final building block of the universe. We used to think they were atoms, but this picture is constantly changing. Thales believed it might be water, and when you look at the quantity of hydrogen in the universe, he wasn’t so far off the mark. But he knew nothing about hydrogen, so this is pure speculation.

The only real point that we can pin down with reasonable certainty is this:

If the smallest conceivable building block of the universe is a piece of material, then this piece must have form. So water must be made of something formed; and when Anaximander looked at this proposition, he spotted a logical contradiction. Any piece of formed matter must logically be divisible; it is inconceivable for a formed thing to be indivisible. Therefore, he reasoned, Thales cannot be right about water. The ultimate particle cannot be a particle; it must be something that is unformed. And so, as an alternative, he proposed a kind of ‘cloud of stuff’ (which he called Apeiron) that becomes matter when it is set in motion: then this element must heat up and split off from the cloud. It need not be water; it could be anything. Two centuries later Democritus picked up this idea and named this element ‘atom’.

From this you are welcome to conclude that Anaximander has the more plausible doctrine.