Illicit major is a
formal fallacy
In logic and philosophical logic, philosophy, a formal fallacy is a pattern of reasoning rendered validity (logic), invalid by a flaw in its logical structure. propositional calculus, Propositional logic, for example, is concerned with the meaning ...
committed in a
categorical syllogism
A syllogism (, ''syllogismos'', 'conclusion, inference') is a kind of logical argument that applies deductive reasoning to arrive at a conclusion based on two propositions that are asserted or assumed to be true.
In its earliest form (define ...
that is
invalid because its
major term is
undistributed in the major premise but distributed in the conclusion.
This fallacy has the following argument form:
#''All A are B''
#''No C are A''
#''Therefore, no C are B''
Example:
#''All dogs are mammals''
#''No cats are dogs''
#''Therefore, no cats are mammals''
In this argument, the major term is "mammals". This is distributed in the conclusion (the last statement) because we are making a claim about a property of ''all'' mammals: that they are not cats. However, it is not distributed in the major premise (the first statement) where we are only talking about a property of ''some'' mammals: Only some mammals are dogs.
The error is in assuming that the converse of the first statement (that all mammals are dogs) is also true.
However, an argument in the following form differs from the above, and is valid (Camestres):
#''All A are B''
#''No B are C''
#''Therefore, no C are A''
See also
*
Illicit minor
*
Syllogistic fallacy
A syllogism (, ''syllogismos'', 'conclusion, inference') is a kind of logical argument that applies deductive reasoning to arrive at a conclusion based on two propositions that are asserted or assumed to be true.
In its earliest form (define ...
External links
Illicit MajorThe Fallacy Files
Syllogistic fallacies
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