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An enthymeme is a logical fallacy in which a categorical syllogism omits a premise that is necessary for the conclusion to be true or omits the conclusion itself. The missing proposition is considered to be implied. Enthymemes are very commonly used in everyday argumentation because the mind usually supplies the missing premise subconsciously; however, they are often used to obscure a bad argument. The term is also used in a broader context to refer to any informal argument that includes unstated assumptions.
While the term existed prior to Aristotle, the author of this article thinks that he was the first to use it in this sense.
 Alternate names
- jumping to conclusions
An example might be something like this:
- Santa will give you presents because you've been a good boy.
This statement assumes that Santa gives presents to good boys. This can be restated formally as:
- P1: (unstated) Santa always gives presents to good boys.
- P2: (stated) You've been a good boy.
- C1: (stated) Therefore, Santa will give you presents.
There is a missing premise, "All that which causes death is evil," that is required to make the logical connection between the first premise and the conclusion. It is important to recognize enthymemes and analyze the implied premise to ensure no false premises are being "slipped under the rug."
 Avoiding the fallacy
Someone can accuse you of jumping to conclusions if you assume something is true without stating it outright, or someone may accuse you of jumping to conclusions merely because he wants to do it, regardless of any commitment to logic. If you wish to convince an audience, you may consider spelling out any assumptions that might not be shared by your audience. But note that you might be asked to defend those assumptions, so it would be wise to prepare what you will say in response and avoid committing a fallacy during the hasty construction of a response. But realize that once you give some proof for an assumption, you have essentially abandoned the assumption, admitting that it is not self-evident and thus not assumable. For logic can assure that your conclusions are valid based on assumptions (givens); but logic has no power whatever to create the assumptions (givens, self-evident truths, axioms).
- "Enthymeme" in "Aristotle's Rhetoric, Stanford Encyclopedia of Philosophy
- Enthymemes: The Elliptical Argument
- Jumping to Conclusions, Internet Encyclopedia of Philosophy
- Alter a pars, Infidels.org