Answer:
speculation.
Step-by-step explanation:
Democritus was a pre-Socratic philosopher. Like all philosophers who share this label, they mostly engaged in a kind of thought governed by speculation in search of governing doctrines, in specific a peculiar form of speculation, that is to say, a kind of informed and well-reasoned imaginative effort based on no empirical or demonstrable principles. One such speculative doctrine is his theory of atoms which holds great resemblance with the modern day conception of atoms that we have today, though they are based on extremely different arguments and, in the case of the Greek philosopher, no observable phenomena.