Thinking through your beliefs is not “ad hoc” . . . At least in a bad way of using “ad hoc.” “Ad hoc reasoning” can mean reasoning for a specific situation, but is commonly used as a negative move on the part of a desperate person. An idea is in trouble so the defender invents all kinds of other concepts he would not have accepted before the criticism to save the original idea. The result is a mess.
I suspect this common usage is lazy thinking on the part of a critic who does not wish to see his opponent answer his “silver bullet” objection. This is a disease in Christian apologetics with critics of atheistic materialism. If one is an atheist and a materialist, then there are implications of those views. If a person is convinced by serious arguments that there is no God and all is matter and energy in mindless motion, then this idea has implications. The atheistic materialist must work out those implications.
One thing that might happen is that those implications contradict reality as the atheist materialist knows it. Human consciousness is a hard problem for atheist materialists, because (as of yet) no secondary theory that is both atheist and materialist (one need not be both!) is widely thought by atheist materialists to do justice to our experience of consciousness. This is a good reason to reconsider the initial ideas, though an atheist materialist is entitled to time to work out a solution . . .especially if he is very convinced atheism and materialism are true.
Truth for an Apologist to Live By: If you claim x and y cannot both be true and your critic shows one plausible way they can in his system, then you were wrong. At best, you can argue that the proposed solution is (itself) implausible, but take care: is it only implausible if you are a theist!
This is also true for any critic of any complex system. A web of beliefs such as Christian theism will have some ideas central to the web, such as the existence of Jesus, and others that are implied by those beliefs, but would not be believed otherwise. I do not think there is a capital of Atlantis, because I do not believe Atlantis exists or ever existed. However, if one had good reason to think Atlantis existed, then one is justified to look for the capital city.
An intolerant man with one web of beliefs might judge some speculations (fringe ideas one examines, but holds lightly) “silly” if held by a man with another web of belief. Fringe ideas are fringe, but they are necessary since often fringe ideas once examined can improve the system. Most fringe beliefs die, but a few go on to a productive life! The ideas a man will consider (barely) will change depending on his central core beliefs: each big worldview will speculate to a different fringe. As a result, one should never use fringe or speculative ideas, labeled as such, to mock or reject a worldview.
When Christians look at other religions, we are tempted to mock fringe or speculative ideas. Beware! Thinking through a worldview, answering critics from ideas already held in the worldview, or even speculating is not “ad hoc” in any bad sense. Let’s discuss with charity toward all and misuse of rhetoric toward none!