Which type of philosophical assumption pertains to the sources of knowledge?

The appropriate philosophical assumption concerning the sources of knowledge is epistemological. This branch of philosophy specifically examines the nature, scope, and limitations of knowledge, focusing on how knowledge is acquired and validated. It addresses questions about the basis of belief, what constitutes justified true belief, and the methods by which we gain knowledge about the world.

In contrast, ontological assumptions deal with the nature of being and existence, exploring what entities exist and how they can be categorized. Metaphysical assumptions extend beyond epistemology to consider the fundamental nature of reality, discussing concepts such as time, space, cause and effect. Ethical assumptions are concerned with moral values and principles, evaluating what is right and wrong in human behavior.

Therefore, the term that best fits the inquiry into the sources of knowledge is indeed epistemological, as it directly addresses how we come to know and understand the world around us.