Often, someone will label a particular piece of reasoning as fallacious when it only resembles a certain fallacy. Ironically, these people themselves are engaging in fallacious reasoning by doing so. When one accuses something of being fallacious, he must know why it is a fallacy. Let me explain.
Whatever reasons from the parts to the whole is fallacious.
But this is not obviously true. In fact, it seems as though clear counterexamples abound. Consider the wall made of red bricks. Every brick in the wall is red; therefore, the wall is red. Why is this fallacious? It is not. Or consider: every part of his car is made of metal; therefore, the car is made of metal. How does one tell the difference? It seems there is a kind of symmetry between objects in acceptable, non-fallacious composition-based reasoning and an asymmetry between those objects in the fallacy. Taking the team example, it could be pointed out that the parts of the team have not always been part of the team, or there may have been other, previous members. When composition is reasoned to symmetrically, however, it seems utterly harmless.
The same holds true for composition’s cousin, division. Whereas composition reasons from the parts to the whole, division reasons from the whole to the parts. If there is a completely red wall made of four large bricks it follows from this fact the bricks are red. This should be obviously legitimate.
It is important to understand when these are fallacious and when they are not because of their ramifications on theistic discussion. I once read a criticism of a Christian objection to the universe’s necessity. The objection was that if the universe was necessary then everything that happens is itself necessary. Since it is rational to accept there are contingent persons and events, it follows the universe is not necessary. The retort was that this was the fallacy of division, reasoning since the universe (the whole) was necessary, everything (the parts) would be necessary. As it turns out, however, this is not fallacious. For if the universe is necessary, then it just entails the events and persons and things that it does have. Furthermore, no other possible worlds (complete descriptions of reality) are really possible at all. But if something appears in no possible world (such as alternate events, places, things, or persons), then by definition it is not possible at all. That which is not possible is necessarily false when expressed as a proposition. Therefore, it follows analytically that if the universe is necessary, then it is impossible that the universe be necessary and things be different than they are.
It seems that nearly all informal fallacies have exceptions. This is important. If we do not recognize the distinctions and differences, we will simply be trained to look at a basic structure of an argument or reasoning, and not at the reasoning itself. This is needed for good apologetics and philosophy!