This study consists of some of the articles that I presented in lectures during my doctoral education and that I wrote for doctoral qualification. For this reason, the chapters I present here are of limited purpose and are related to lectures. Although it is written in a narrow scope, it still carries a whole in itself. In particular, only those related to epistemology from the studies are brought together and presented here. I hope it will give the reader an insight and perspective in the field of epistemology.