To guard against this and all similar fallacies it is only necessary to notice whether the comparison is fair and complete. Practice will give great expertness in doing this, even when the comparison is implied rather than expressed.
Indeed, the greater part of reasoning lies outside the range of formal logic. The orator who would reduce each argument to a syllogistic form would be considered a clown endeavoring to make sport of, or for his audience. A statement is often made which depends for its validity upon a comparison or even a series of comparisons either flashing through the mind at the moment, or recalled as having previously been made. To this there can be no objection, provided such comparisons are obvious and indisputable. If a chain of reasoning rests upon the understanding that all men desire to be happy, it will be just as forcible as if that truism were stated or proved. Anything which an audience will accept without question is only weakened by the processes of proof. Something must be taken for granted in all kinds of argument, and the wider the domain of such assumptions can be fairly made the better for the interest and effectiveness of the arguments which follow.
A syllogism in which one of the essential parts is left to be supplied in the mind is called an enthymeme, and is the most common of all forms of reasoning. Whenever we state a fact, and adduce a reason for that fact, it takes this form. As an instance, we may give the beatitudes in the fifth chapter of St. Matthew. In each we have a declaration made and a reason given for that declaration, but that reason would have no necessary validity were it not for a well-understood principle, upon which, in each case, it is founded. When it is said, “Blessed are the poor in spirit; for theirs is the kingdom of heaven,” we mentally add, or concede even without thinking it, “whoever has the kingdom of heaven is blessed.”
The same declaration may be put in logical form, thus:
Whoever possesses the kingdom of heaven is blessed.
The poor in spirit possess the kingdom of heaven.
Therefore, they are blessed.
It will be noticed that in all the beatitudes the syllogism is inverted, the conclusion coming first (which also is placed in an inverted form), while the major premise is left to be mentally supplied.
Another instance may be given of this most common of all the syllogistic forms—the only one of which the orator makes very frequent use.
It is stated, “Blessed are the pure in heart; for they shall see God;” the reader mentally supplies, “and those who see God are blessed.”