structure for 'Formal Logic'    |     alphabetical list of themes    |     unexpand these ideas

4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / a. Symbols of PC

[meanings of the symbols used in predicate logic]

4 ideas
Write '(∀x)(...)' to mean 'take any x: then...', and '(∃x)(...)' to mean 'there is an x such that....' [Lemmon]
     Full Idea: Just as '(∀x)(...)' is to mean 'take any x: then....', so we write '(∃x)(...)' to mean 'there is an x such that....'
     From: E.J. Lemmon (Beginning Logic [1965], 3.1)
     A reaction: [Actually Lemmon gives the universal quantifier symbol as '(x)', but the inverted A ('∀') seems to have replaced it these days]
'Gm' says m has property G, and 'Pmn' says m has relation P to n [Lemmon]
     Full Idea: A predicate letter followed by one name expresses a property ('Gm'), and a predicate-letter followed by two names expresses a relation ('Pmn'). We could write 'Pmno' for a complex relation like betweenness.
     From: E.J. Lemmon (Beginning Logic [1965], 3.1)
The 'symbols' are bracket, connective, term, variable, predicate letter, reverse-E [Lemmon]
     Full Idea: I define a 'symbol' (of the predicate calculus) as either a bracket or a logical connective or a term or an individual variable or a predicate-letter or reverse-E (∃).
     From: E.J. Lemmon (Beginning Logic [1965], 4.1)
'⊃' ('if...then') is used with the definition 'Px ⊃ Qx' is short for '¬(Px & ¬Qx)' [Putnam]
     Full Idea: The symbol '⊃' (read 'if...then') is used with the definition 'Px ⊃ Qx' ('if Px then Qx') is short for '¬(Px & ¬Qx)'.
     From: Hilary Putnam (Philosophy of Logic [1971], Ch.3)
     A reaction: So ⊃ and → are just abbreviations, and not really a proper part of the language. Notoriously, though, this is quite a long way from what 'if...then' means in ordinary English, and it leads to paradoxical oddities.