Gorgias of Leontini in Sicily (c. 485–380 B.C.E.) taught the art of persuasion for success in politics. His surviving treatise “Of That Which Is Not; or, On Nature” claims that nothing truly is. Although, even if anything were to exist, it could not be comprehended by man; and even if it could be comprehended, it could not be communicated. Just because we have a thought about something does not mean that thing exists. Thoughts do not entail the existence of what is thought, or else humans could not think about, for instance, imaginary animals. Or in other words, not everything we think about exists or is real. Therefore, Gorgias concluded, if anything exists, it cannot be thought. The same gap between thoughts and things occurs between words and things and between the thoughts of different human beings.