So far, I have discussed knowledge in general and in the various sciences. I have briefly mentioned skepticism when I discussed the difference between experiential, factual and theoretical knowledge, but I cannot really finish a series on knowledge without discussing skepticism.
There are special and general forms of skepticism. The special forms of skepticism are all skepticism about knowledge. They are special because knowledge varies depending on which discipline is being discussed. So a skepticism about scientific knowledge need not lead to a skepticism about philosophical knowledge. The general form of skepticism is not a skepticism about theoretical knowledge of some kind but about experiential knowledge. This includes skepticism about perception, memory or any other sense as well as skepticism about our ability to join that knowledge to create facts.
The special form of skepticism is not properly resolved in a general discussion on knowledge. We would first need to establish what science we are being skeptical of and what knowledge is in that science before the skepticism could be resolved. Since knowledge varies across all of the sciences, the resolution to skepticism may vary as well. We could not rule such a thing out before investigating it.
The general form of skepticism can be divided into two categories. The first category is related to the senses. A skeptic may believe that our senses are the source of skeptical worries. Perhaps they are unreliable. Perhaps they are generally reliable, but are occasionally unreliable and we cannot tell the difference. Perhaps there is some other problem. The second category is related to facts. Perhaps the problem is not with our senses. Perhaps the problem is that we cannot gain facts from our sense information. Perhaps there is no reliable way of gaining true facts from our sense information. Perhaps there is a related problem.
There is also a general argument against such skeptical worries. It is very simple. There needs to be evidence to justify any skeptical claim. There are two ways that skeptical worries could be stated. The first way is simply by means of doubt. The claim is not that the senses are unreliable, but that such a claim deserves serious consideration. The second is a demand for evidence. It is the claim that the senses are unreliable, not just that they may be unreliable. But claims are only worth consideration if there is a reason to consider them. We do not seriously consider the claim that the moon is made out of cheese because there is no reason at all to make that claim. Similarly, any skeptical claim of either sort requires evidence to even be considered. But skepticism is not unified in the same way as knowledge. So acceptance of one skeptical claim does not make further claims more acceptable. Therefore, each skeptical claim can only be considered if there is evidence to consider it. There mere presence of worries is not sufficient.
To say more on this matter would require a digression into human psychology and perception.