Maverick Philosopher

Footnotes to Plato from the foothills of the Superstition Mountains

David Brightly’s Weblog and a Punctilio Anent Predication and Inclusion

The unduly modest David Brightly has begun a weblog entitled tillyandlola, "scribblings of no consequence."   In a recent post he criticizes my analysis of the invalidity of the argument: Man is a species; Socrates is a man; ergo, Socrates is a species.  I claimed that the argument equivocates on 'is.'  In the major premise, 'is' expresses a relation of conceptual inclusion: the concept man includes the subconcept species.  In the minor premise, however, the 'is' is the 'is' of predication: Socrates falls under man, he doesn't fall within it.

I am afraid that my analysis is faulty, however, and for the reasons that David gives.  There is of course a difference between the 'is' of inclusion and the 'is' of predication.  'Man is an animal' expresses the inclusion of the concept animal within the concept man.  'Socrates is a man,' however, does something different: it expresses the  fact that Socrates falls under the concept man. 

But as David notes, it is not clear that species is included within the concept man.  If we climb the tree of Porphyry we will ascend from man to mammal to animal; but nowhere in our ascent will we hit upon species. 

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Bill Vallicella

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2 responses to “David Brightly’s Weblog and a Punctilio Anent Predication and Inclusion”

  1. duffe Avatar
    duffe

    Man is a species (logical supposition)
    Socrates is a man (real supposition)
    Therefore, Socrates is a species.
    Iirc & fwiw, medieval logicians would say the major is in logical supposition (has only mental existence) because the predicate cannot be passed on from the universal to the singular. The minor is in real supposition (has real existence) since the predicate can accept singulars. Hence, the syllogism is invalid because even though the middle-term ‘man’ is the same term it’s meaning (mode of existence, i.e. mental v. real) is different in the major and minor, resulting in the syllogism becoming a logical quadruped.

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  2. peterlupu Avatar
    peterlupu

    Bill,
    Perhaps we could construe species as a second-order property of man rather than as a concept included in the concept *man*.
    Another possibility is to think of ‘species’ as an undetachable modifier predicate of the predicate ‘man’. For instance, in ‘x is a short basketball player’, the predicate ‘short’ modifies ‘basketball player’ and therefore one cannot infer from the sentence ‘x is a short basketball player’ the sentence ‘x is short’.
    Both methods might avoid David’s problem and preserve your intuition that the species inference is invalid.

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