Everything changes constantly. You can never step into the same river twice!
Impossible! A substance would have to transition through nothing to become something else, which is a logical contradiction.
How can matter change and still exist? Enter Democritus...
You're both wrong!
He hypothesized that all matter (plus space and time) is composed of tiny indestructible units, called atoms. This idea seems motivated by the question of how finely one can go on cutting up matter.
Matter is made up of indistructable units, I like to call them atoms! The atoms in themselves remain unchanged, but move about in space to combine in various ways to form all macroscopic objects. The characteristics of an object are determined by the shape of its atoms. So, for example, sweet things are made of smooth atoms, bitter things are made of sharp atoms.
Greek philosophers, Heraclitus and Parmenides debated matter. Like other philosophers of their time, they tried to theorize what makes up the world around them. Many of their ideas conflicted. While Heraclitus believed everything was constantly changing, Parmendies argued that was a logical impossibility!
So there was a problem, how could matter change and still exist? An ingenious escape was proposed in the fifth century B.C.E by Democritus.
While Democritus performed no experiments and had only the flimsiest evidence for postulating the existence of atoms, his theory was kept alive by the Roman poet Lucretius. The atoms in Democritus theory themselves remain unchanged, but move about in space to combine in various ways to form all macroscopic objects. Early atomic theory stated that the characteristics of an object are determined by the shape of its atoms.