In order to answer this question, we should first look at what epistemology is. Epistemology is the study of knowledge. Epistemology asks what it means to know something. It asks how we can know things and what knowledge is. Various epistemologies, such as positivism and idealism, answer these questions in different ways.
Idealism is an epistemology that believes in the importance of a person’s own perceptions. To an idealist, knowledge only exists in our own minds. The only things that we can know are things that we can perceive in our minds. There is no reality that is independent of our minds.
Positivism takes a different point of view. To positivists, there are real truths that are independent of what one perceives. The best way to get at these truths is through the scientific method. If one uses scientific methodologies along with rational and logical thought, one can uncover actual truths.
Thus, these are two very different epistemologies. One holds that there are real truths that can be discovered through science while the other argues that the only things we can know are things that are in our own minds.