... Every human, after all, accepts the reliability of the senses and the existence of the external world, not by a logical inference from the effect, in this case the representation in his consciousness, to the cause outside of himself, nor by reasoning from the resistance his will encounters to an objective reality that generates this resistance. Prior to all reflection and reasoning, everyone is in fact fully assured of the real existence of the world.
This certainty is not born out of a syllogism, nor is it supported by proof; it is immediate, originating, spontaneously within us along with perception itself. It is not a product but the foundation and starting point of all other certainty. Every human, even the least knowledgeable, a child already and an animal also, accepts in advance, without any reasoning, the existence of an external world. [Herman Bavinck, Reformed Dogmatics, 1: 223]
In his response to Rationalism and Empiricism, the theologian Herman Bavinck embraced some form of Realism, which in our day would be called "Reformed Epistemology." His argument for accepting some things as basically true, viz the reliability of the senses and the existence of the external world, seem valid. After all, is it not true that humans basically "know" these to be true before any reflection and reasoning?
Unfortunately, things aren't always that easy. Yes, it is admitted that humans operate under these beliefs prior to reflection and reasoning. Yet, it is one thing to say that they operate on that level, and another thing to say that they accept these to be true. The former is self-evident, the latter we deny. The fact is that unreflective human beings do not "accept" these to be true, because they have not made a self-conscious epistemic commitment to the truth value of these statements. They operate on that level, but not because of acceptance of the truth of these two claims: that (1) the senses are reliable, and (2) the external world really existed. Being unreflective, they do not have a position on the issue beyond a knee-jerk affirmation if pressed on the issue.
Now, that humans operate as if Realism is true needs to be explained. It could be explained by Realism, or perhaps by other theories. Of course as a Christian, we should affirm Realism, but the question is why we should affirm Realism. The "Reformed Epistemology" view does a disservice here because it jumps directly to Realism, with arguments similar to the ones Bavinck puts forward. But such arguments for realism are not convincing, for reasons like those I have posted.
Christianity teaches Realism, but just because we agree on the conclusion does not mean we agree on the arguments put forward for it. The response which I think is the right one is to say that Christianity teaches Realism because the Scriptures teaches it, not that it is the default view we should adopt.