Consider the brain in a vat scenario. A powerful scientist could be feeding impulses from a simulation into your brain in exactly the same way as if your brain was in a skull, rendering you unable to determine if the world you perceive actually extends beyond your potentially simulated or deceptive perceptions.
This isn't exactly full blown solipsism, but it establishes a primitive case which can cast some (albeit minimal) doubt on whether or not our perceptions even indirectly reflect an external or objective world.
Skepticism can really do away with a lot if it is applied to the extreme, but luckily pragmatism regularly steps in and sets us straight. — VagabondSpectre
Your brain in a vat example does not cast doubt on whether or not there is an external world. There is still the need for your "powerful scientist" feeding impulses. The scientist comprises an external world. It is just that in this example, the real external world is not anything like the external world as the brain in the vat perceives it.
That is what I've been arguing is really the case, the real external world isn't anything like the way that we perceive, and describe it. That is evident from the example which we've already discussed, "the sun rises". The description refers to what we perceive, but we now know that what we perceive is not anything like what is really the case. We could extend this to our understanding of substance in general, molecules and atoms etc., what we perceive is completely different from what is really the case. Since this extreme difference exists, between how we perceive, and describe, the external world, and what we've determined is really the case, it may just as well be a brain in the vat scenario. We still haven't gotten beyond analyzing the impulses, understanding them well enough, to the point of determining the necessity for a "powerful scientist" sending us these impulses.
How we've progressed in this discussion, you and I, has been painfully slow, because we each have vastly differing perspectives on this. You want to assume that consistency in observations implies necessarily that there is consistency in the external world, but we haven't accounted for the brain itself, which in this example is assumed to be in a vat. So let's start with a real skeptic's position, let's assume that it is possible that there is no scientist at all, absolutely nothing external, just a mind, and the mind itself is producing all the images of perception.
Notice that I introduce this premise as a possibility. This is to counter your assumption that consistency in observation necessarily implies consistency in the thing observed. If we allow that the mind itself is capable of creating, and this is what is implied by the concept of free will, that the mind can create without the necessity for external causation, then it is possible that the observed consistency is completely created by the mind.
This is the point which I've been attempting to bring to your attention. If we allow the principles of free will, we allow that the mind itself creates without external cause. So when we proceed to analyze consistency in observations, we need to be able to distinguish which aspects of that consistency are created by the mind, and which aspects are proper to the thing being observed.
This is why we need to consider semantics, the words which we use, and the ways in which we describe things, as having real influence over the observations which we make, and especially the consistencies which we observe. I say this because it is clear that we actually seek consistencies, as consistency is what leads to understanding, so we describe things in terms of consistency. But of all particular things, in general, there are differences and similarities between them. We may overlook the differences to focus on the similarities. And this is what happens with our habitual word use, we call things by the same name, because they are similar in some way, overlooking the differences, and this creates consistency. The use of the same word to describe different things creates an illusion of consistency, through overlooking the differences.
So for instance we say "the sun rises in the east". This is a statement of consistency. However, each day the sun will appear to come up in a slightly different location on the horizon. So the sun isn't consistently rising in the same place, directly to the east, it varies from south to north, despite the fact that we say it rises consistently in the east. We create a generalization, overlooking the various differences, and say that the sun rises in the east. Now we have a consistency which has been created by this generalization, which acts as a description of many slightly different occurrences, describing them all with the very same words, "the sun rises in the east". This consistency has been created by our mode of description, which is to overlook slight differences, and focus on similarities. However, overlooking the inconsistencies, to focus on the consistency, produces a false consistency. It is necessary to negate this false consistency "the sun rises in the east", and focus on all the slight inconsistencies, in order to truly understand the relationship between the earth and the sun.
You think pragmatism sets us straight, but that is not the case at all. Pragmatism is what inclines us to create consistencies, and in creating these consistencies the real inconsistencies are hidden. By loosing track of the real inconsistencies through the claim of consistency, misunderstanding thrives.