In contemporary philosophy the main question is that knowledge is not a true belief but rather a true justified belief.
By distinguishing between understanding and knowledge, the author of this article is going to explain that for understanding a proposition one should understand the reason of truth of that proposition. He also applies Humean instrumental approach toward knowledge, in which reason is a servant of emotions, to clarify Aristotle and Plato’s point of view in this respect. He finally distinguishes between practical and theoretical reason and following Rescher maintains that cognitive, evaluative and practical rationality relies upon one another. At the end he concludes that we cannot find a unified notion about rationality. So we can understand that human being is more than a single integrated intellect. This is the subject that should be noted in modern epistemology.