It is maintained that epistemological skepticism is different in theme and scope. There are two types of skepticism: knowledge skepticism and justification skepticism (Moser et al, 1998). While unlimited knowledge skepticism suggests that “no one knows anything including the claim itself” (reference), unlimited justification skepticism suggests a radical point of view that “no one is even justified in believing anything including this view itself” (reference).
Epistemological skepticism differs in theme and scope. Two noteworthy types of skepticism are recognized: knowledge skepticism and justification skepticism (Moser et al., 1998). Unrestricted knowledge skepticism implies that no one knows anything including this claim itself. Unrestricted justification skepticism implies extreme view that no one is even justified in believing anything including this view itself.
Another discrepancy is related to the level of skepticism. In its first level, skepticism claims that it impossible for an individual to know anything. In its second level, skepticism proposes that an individual does not know that he has knowledge. I t is probably that one knows P, but he does not know that he knows P ( Brenecker and Dretske, 2000).
The other difference concerns the order or level of skepticism. In its strongest form, first order (or direct) skepticism implies that it is [impossible of] logically impossible for anyone to know anything. Second order (or iterative) skepticism is a weaker thesis that we cannot know that we have knowledge. Maybe you know P, maybe you do not, but you cannot know that you know P (Brenecker and Dretske, 2000).
Regardless of the shape or size taken by skepticism, it is believed that is stimulated by one sole thing: seeking unlimited knowledge.
Whatever form or magnitude skepticism takes, it is thought to be motivated by one thing; the search for true unrestricted knowledge.
Pyrrhonians utilized skepticism in their search for true knowledge, which led them to suspending judgment of truth. However, ancient skepticism used to be unlimited with no conditions. It is believed that ancient skepticism is “motivated by the nature of social and intellectual turmoil that existed in those times which invited deep questions about right and wrong, and truth and false” (reference). Ancient skepticism placed for discussion more extreme doubts and maintained more radical attitudes than those familiar in modern skepticism. For instance, Sextus uses Gorgias’ argument to conclude “that nothing exists (and that if it did we could not know so, and that we could not communicate it even if we knew” (reference). (1)
Skeptics in the ancient world particularly Pyrrhonians deployed skeptical behavior in the infinite quest for knowledge and truth. They suspended judgment of truth of any claim. Ancient skepticism was unrestricted and unconditional. It is believed [Thought] to be motivated by the nature of social and intellectual turmoil that existed in those times which invited deep questions about right and wrong, and truth and false. Ancient [ancient] skepticism raised more radical doubts and adopted more extreme positions than those we see in modern skepticism. An example which Sextus favors is Gorgias’ argument for the conclusion that nothing exists (and that if it did we could not know so, and that we could not communicate it even if we knew)  .
The basic themes of ancient skepticism are “belief, suspension of judgment, criterion of truth, appearances, and investigation” (reference). However, modern skepticism mainly focuses on “knowledge, certainty, justified belief, and doubt” (reference). (2)
The core concepts of ancient skepticism are belief, suspension of judgment, criterion of truth, appearances, and investigation. Modern skepticism is more concerned about knowledge, certainty, justified belief, and doubt  .
The skeptical challenge has indeed many sources in the epistemological context. One of these sources is that we obtain our knowledge about the outside world through senses. We, however, may be deceived by these senses, and therefore, skepticism, due to “the epistemic priority of the senses”, becomes an unavoidable issue (Okasha, 2003).
There are many sources or root causes for the skeptical challenge in the epistemological context. One such source is the fact that knowledge about the external world is principally informed by senses. As we will see later, those senses might deceive us in many ways. The “epistemic priority of the senses” makes skepticism unavoidable (Okasha, 2003).
The epistemic priority of the senses has indeed a catastrophic effect on the human knowledge. When we agree that one type of knowledge comes before another as an underlying component of our philosophical understanding, we cannot be satisfied by a different idea (Stroud, 1989).
(Stroud, 1989) believes that such epistemic priority has fatal consequences on the understanding of human knowledge. Stroud argues that “once we accept the idea that one kind of knowledge being prior to another as an essential ingredient in the kind of philosophical understanding we seek, it immediately becomes difficult to imagine, let alone to find anything that could satisfy us” (1989, p. 312).