Maverick Philosopher

Footnotes to Plato from the foothills of the Superstition Mountains

Category: Logica Docens

  • Logical Form and the Symmetry Thesis

    "The most conspicuous purpose of logic, in its applications to science and everyday discourse, is the justification and criticism of inference." (Emphasis added, Willard Van Orman Quine, Methods of Logic, 2nd revised ed., Holt, Rinehart & Winston, 1959, p. 33. Perhaps the dispute in the earlier thread could be resolved if we all could agree…

  • The Logic of Buddhist Philosophy

    Beyond True and False, by Graham Priest. (HT: Allan Jackson)

  • Logical Form and the Supposed Asymmetry of Validity and Invalidity: A Defense of Symmetry

    For the 'Londonistas,'  Ed and David, partners in logical investigations.  We are unlikely ever to agree, but clarification of differences is an attainable and worthwhile goal, here, and in every arena of controversy.  Have at it, boys. …………. 1. Suppose someone reasons as follows. 'Some Englishmen are Londoners; therefore, some Londoners are Englishmen.'  To reason…

  • Lukasiewicz on Logical Form

    London Ed writes, I read and excerpted the chapter. I am not mistaken. Also, what he says seems correct to me. He claims that logic is not formal, insofar as it is concerned with the 'laws of thought'. He says "Thought is a psychical phenomenon, and psychical phenomena have no extension. What is meant by…

  • Logical Form, Instantiation, and Pattern-Matching

    David Brightly comments: We can't say that an argument is invalid because it instantiates an invalid form. The argument Socrates is a man; all men are mortal; ergo Socrates is mortal instantiates the invalid form a is F; all Hs are G; ergo a is G, but modulo equivocation, it is truth-preserving. Instantiation of form…

  • Validity and Semantics: Will the Real Frodo Baggins Please Stand Up?

    London Ed writes, It is a well-known and puzzling fact that proper names are ambiguous. According to the US telephone directory, Frodo Baggins is a real person (who lives in Ohio). But according to LOTR, Frodo Baggins is a hobbit. Not a problem. The name ‘Frodo Baggins’ as used in LOTR, clearly has a different…

  • On the Enforcing and Permitting of Coreferentiality by Argument-Forms

    This argument is invalid: Cicero was a RomanTully was a philosopher—–Some Roman was a philosopher. Quite simply, there is no middle term. The example is an instance of the dreaded quaternio terminorum. But of course we learned at Uncle Willard's knee that Cicero = Tully. Add that fact as a premise and the above argument…

  • How to ‘Derive’ Ought from Is

    I demanded an argument valid in point of logical form all of whose premises are purely factual but whose conclusion is categorically (as opposed to hypothetically or conditionally) normative.  Recall that a factual proposition is one which, whether true or false, purports to record a fact,  and that a purely factual proposition is a factual…

  • Three More Putative Instances of Valid Is-Ought Inferences

    I thank Tully Borland for pushing the discussion in this fascinating direction. A Affirming the Consequent is an invalid argument form.ErgoOne ought not (it is obligatory that one not) give arguments having that form. B Modus Ponens is validErgoOne may (it is permissible to) give arguments having that form. C Correct deductive reasoning is in…

  • Syntactic Versus Semantic Validity

    Consider the argument:     Bill is a brother   —–   Bill is a sibling. Is this little argument valid or invalid?  It depends on what we mean by 'valid.' Intuitively, the argument is valid in the following generic sense:    D1. An argument is (generically) valid iff it is impossible that its premise(s) be true and…

  • The Stromboli Puzzle Revisited

    Here is a little puzzle I call the Stromboli Puzzle.  An earlier post on this topic was defective.  So I return to the topic.  The puzzle  brings out some of the issues surrounding existence.  Consider the following argument. Stromboli exists.Stromboli is an island volcano.ErgoAn island volcano exists. This is a sound argument: the premises are…

  • *Every Proposition is Affirmative*

    Nicholas Rescher cites this example from Buridan.  The proposition is false, but not self-refuting.  If every proposition is affirmative, then of course *Every proposition is affirmative* is affirmative.  The self-reference seems innocuous, a case of self-instantiation. But *Every proposition is affirmative* has as a logical consequence *No proposition is negative.*  This follows by Obversion, assuming…

  • Amphiboly of the Day: ‘Pretty Bad Girls’

    An amphiboly is a syntactic ambiguity.  Are they pretty and bad, or pretty bad? Related articles Pseudo-Latin French Bullshit: The Cartesian Castle

  • Existence-Blindness or Double-Vision?

    I had the pleasure of meeting London Ed, not in London, but  in Prague, in person, a few days ago.  Ed, a.k.a. 'Ockham,' and I have been arguing over existence for years.  So far he has said nothing to budge me from my position.  Perhaps some day he will.  The following entry, from the old…

  • Vallicella on the Argument for God from Logic

    James Anderson responds here to my critique of his and Greg Welty's The Lord of Non-Contradiction: An Argument for God from Logic. Professor Anderson's combox is open.