For a specific purpose only; as, an ad hoc investigative committee.
< Latin (for this).

Roughly translated as "this case" or "this time". A common fallacy of logic in which evidence that refutes a theory is addressed by a one-shot explanation that only addresses those specific cases. See also the No True Scotsman fallacy.

Ad Hoc is a Latin phrase that literally translates to "for this" and 'formed with a particular purpose". Ad hoc can be anything that it thrown together temporarily.

A really good way to remember ad hoc, is that it is a term used for committees in the House of Representatives that are in place to fulfil a short term goal and are then dissolved.

I was in a political science class a few semesters back. I adored the teacher I had, and am planning on taking another one of his classes (no, I am not addicted, this will only be my third). Anyway, this teacher liked to use words that many of us students hadn't ever heard before, he liked to use words that expanded our minds, he liked to use words that made him sound over-educated and pretentious. He was great. I liked to ask him what these words meant; he threatened to buy me a dictionary.

This professor while teaching us about American political systems used the term ad hoc to describe committees in the House of Representatives that were temporary, and put in place to fulfil a short term goal, and then dissolved when no longer needed.

So, what can I say? I liked what I was learning in this class. I too wanted to sound well educated and pretentious. Yes, I started to use the term ad hoc as well. If you are around me long enough, you will catch me using it now and again, but don't ask me to use it in a sentence right then and there because you will probably get something like. 'You expect to me to use it so ad hoc that I cannot think of a really good sentence to use it in!"

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The ad hoc fallacy needs a bit more explanation. It is generally encouraged for scientists (and other humans) to come up with explanations explaining specific cases, and to explain away abnormalities in empirical observations. Urbain Leverrier, for example, theorized an eighth planet in our solar system, in an attempt to explain variations in Uranus' expected flight path. It turns out that he was right; Neptune was affecting Uranus' orbit. Neptune was, in a very strong sense, an ad hoc hypothesis attempting to patch up an apparent hole in the theories of gravitation and Kepler’s laws.

But while ad hoc may be A Good Thing, it can be over-applied. I might claim that there are humans who have ESP abilities, and that I have shown it in controlled experiments. Why can't these experiments be duplicated? Because the hostile thoughts of sceptics disrupt this ability; because using a experimental setup the subjects are not used to throws them off-stride; because the planets were in a bad alignment that day... Any or all of these might be true, but there comes a point where it is no longer productive for mainstream science to research, or believe in, ESP. The fallacy ad hoc comes into play when the ad hoc explanations become too plentiful, too unbelievable, too untestable, and too unproductive. (You will note that Leverrier discovered a planet with his hypothesis... Now that's good ad hoc.)

Ad hoc is a rather subjective fallacy, but one people tend to put a lot of weight on. Watch out for those accusing others of this -- they are often right, but think it though for yourself.

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