In Aristotle, different types of knowledge are possible concerning different types of subject matter. True knowledge, or episteme, is only possible with respect to unchanging scientific or mathematical truths, which can be proven by using logic from premisses that cannot be otherwise. The type of speech appropriate to scientific knowledge is apodeictic, or demonstration. Matters concerning ethics or how we should conduct our lives are the prvince of practical wisdom or phronesis. Like all things which can be otherwise, they can be disputed using dialectic, which is the art of reasoning about the probable. While dialectic approaches the art of the probable using techniques of logic to uncover valid argument, we employ rhetoric when we wish to persuade an audience. In matters such as ethics, since there is no certain knowledge, one source of information is endoxa, or the opinions of the wise.