There are two kinds of knowing, the one he calls "legitimate" (γνησίη, "gnēsiē", "genuine") and the other "bastard" (σκοτίη, "skotiē", "secret"). The "bastard" knowledge is concerned with the perception through the senses; therefore it is insufficient and subjective. The reason is that the sensual perception is due to the effluences of the atoms from the objects to the senses. When these different shapes of atoms come to us, they stimulate our senses according to their shape, and our sensual impressions arise from those stimulations.