You keep using that word. I do not think it means what you think it means.

In Rob Reiner's masterpiece, The Princess Bride, the character of Vizzini keeps using the word 'inconceivable' to describe things that have already happened. In the clip above, Inigo Montoya calls him out on it, suggesting that Vizzini isn't quite as smart as he thinks he is. This raises an important point about definitions and about being careful in one's choice of words, seeking to pick the best word for the situation, something Vizzini clearly fails at.

An important fallacy that revolves around the misuse of words and their definitions is Equivocation. This is a fallacy arising from the misuse of words that have more than one meaning or denotation (the dictionary meaning of a word; the objects to which the word refers). This fallacy generally arises when a word is used with one meaning in one part of the argument and then a different meaning in another part of the argument.

I found several nice examples of this fallacy in an article published on Answers in Genesis, a creationist, anti-evolution website. In an article published today, Bodie Hodge takes issue with an editorial in the NewScientist discussing secular approaches to morality (oddly enough, Answers in Genesis does not link to the article in question though they do provide a reference for it). There are many fallacies in this short article, but I want to focus on the Equivocations. The first example can be found when Hodges writes:

Next they say, “Altruism for example can benefit your genes and disgust can protect you from disease.” What do they mean by “benefit”? Did you catch that? They are appealing to some overarching “good” in the universe by which to judge something as a “benefit.” Secularists are borrowing from the biblical worldview when they propose that something such as a “benefit” or “good” exists. By so doing, they undercut the very argument they are trying to propose.

The equivocation here is with the word "benefit." In the context of the NewScientist article, the word is clearly meant to be understood in an evolutionary context in the sense that altruism can confer a survival advantage on entities that possess that trait. That is, entities that are altruistic are more likely to survive and reproduce and pass this trait onto their offspring. This is really a non-moral use of the word 'benefit', but Hodges misinterprets this word as making a moral claim with respect to some transcendent moral standard. Interestingly enough, the author of the editorial explicitly avoids moral terms like "good" in favor of a non-moral term like "benefit" yet Hodges still equivocates.

We can see a similar Equivocation in the next paragraph when Hodges argues:

Furthermore, who are these people to say that “disgust” is a good thing or that being disease-free is a good thing? Such ideas are a reflection of Leviticus and the cleanliness laws from the Bible, which teaches to resist effects of a sin-cursed and broken world. But how can an evolutionist say that preventing disease is a good thing? Perhaps catching a disease and dying is what is needed for the next step of evolution.

I must first note that the NewScientist editorial never says that disgust or being disease-free are good things. All the author is saying is that disgust can be a useful attitude because it can help organisms avoid substances which can be potential vectors for disease. From the standpoint of the organism in question this is useful as avoiding disease increases the chance of survival and reproduction, but again, these are clearly non-moral concepts. Hodges, however, equivocates and tries to give this word a moral sense.

Hodges continues his deliberate equivocations in the next paragraph:

Next, they comment that “this picture is progress, but it can also lead to a kind of fatalism, a belief that our moral values evolved for a good reason and so we should stick with them.” So, now they are appealing to an overarching concept of “good” by which to judge these things? For people who claim that they no longer believe in morality being “handed down from on high,” they have twice appealed to something higher that determines what is good and bad and governs everything. This is self-refuting!

In this case, the author of the editorial does actually use the word "good" but it is again being used in a non-moral sense. The "good reason" referred to is clearly intended to be interpreted in evolutionary terms, but Hodges again equivocates and assumes that it is being used to refer to some transcendent moral standard, leading him to accuse the NewScientist of begging the question or being inconsistent.

In summary, the editorial in the NewScientist uses a number of terms that are clearly intended to be non-moral concepts that should be understood in evolutionary terms, but Hodges deliberately misinterprets them to be referring to moral concepts. This is a clear case of Equivocation in that the word is being used with one meaning by the NewScientist but then is being given a completely different meaning by Hodges in order to draw a conclusion critical of the NewScientist. Hodges keeps using that word. But, in this context I do not think it means what he thinks it means.