a fortiori

An argument in which a rhetor reaches a conclusion by first setting up two possibilities, one of which is more probable than the other. Whatever can be affirmed about the less probable can be affirmed with even greater force about the more probable.

Etymology

From the Latin, "from the stronger"

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Reductio Ad Absurdum in Argument

By Richard Nordquist

Examples and Observations

"Remember the commercial for Life Cereal, the one where the brothers experiment on picky little Mikey? If Mikey liked it, the boys figured, anyone would. That's an argument a fortiori: If something less likely is true, then something more likely will probably be true as well."
(Jay Heinrich, "If Bill Had Great Interns, Then Hillary . . ." Figures of Speech Served Fresh, August 1, 2005)

"The concept underlying this phrase can be illustrated thus: if you do not trust your child to safely operate a bicycle, then a fortiori, you do not trust him to operate an automobile.

"This 'with stronger reason' argument implies a comparison of values. The argument is grounded on the common sense (and logical) convention that within the same category the greater includes the lesser (or, if you will, the stronger includes the weaker). Do not let the use of the word 'includes' mislead you. Because one person is taller than another does not mean the other is included within the one. The comparison is not between physical things, but between the relative values of actions, relationships, principles, or rules. When you make or analyze this type of argument, do not mix apples and oranges. The comparison should be one of factually like things and be factually meaningful. The objects of the comparison must share essential factual elements if they are to be of like kind. You may not trust your child to operate a bicycle safely, but that does not necessarily mean that he cannot be trusted to bring in the groceries."
(Ron Villanova, Legal Methods: A Guide for Paralegals and Law Students. Llumina Press, 1999)

"It is an argument a fortiori, 'from the stronger.' If I show you that two is less than ten then it is easy to persuade you a fortiori that two is less than twenty. If I show you that what you think is a burden of the welfare state is actually small, or badly estimated, or a benefit, then it is less difficult to persuade you that rolling back the welfare state requires sober thinking about the alternatives."
(Stephen Ziliak, review of The Economic Consequences of Rolling Back the Welfare State. Journal of Economic Literature, March 2001)

"I feel that it is my civic duty to pay my taxes as well as my other bills, and that it is my moral duty to make an honest declaration of my income to the income tax authorities. But I do not feel that I and my fellow citizens have a religious duty to sacrifice our lives in war on behalf of our own state, and, a fortiori, I do not feel that we have an obligation or a right to kill and maim citizens of other states or to devastate their land."
(Arnold Toynbee)

Pronunciation: a-FOR-tee-OR-ee