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The Language P

The Language P. 8 9 ( 8 x) ( 9 y) ( 8 z) 9 8. Quantificational Logic.

joshua-finley
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The Language P

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  1. The Language P 89 (8x) (9y)(8z) 9 8

  2. Quantificational Logic Quantificational Logic:Quantificational Logic is the logic of sentences involving quantifiers, predicates, and names. We will study the properties which arguments and sentences have in virtue of their quantificational structure.

  3. Predicates and Singular Terms • Socrates is human • Plato is human • Socrates is bald • The inventor of Velcro is bald • The inventor of Velcro kills Plato • Socrates kills Socrates • Seven is less than twenty • Socrates introduces Plato to the inventor of Velcro • The least prime number is between seven and twenty

  4. Singular Terms Singular Term:A singular term is a word or phrase which designates or is supposed to designate some individual object. Natural language singular terms are either proper nouns or definite descriptions (a phrase which is supposed to designate an object via a unique description of it). From the previous slide: • Socrates • Plato • the inventor of Velcro • seven • twenty • the least prime number

  5. Predicates Predicate:A predicate is a series of words with one or more blanks which yields a sentence when all its blanks are filled with singular terms. Conversely, we could think of a predicate as what remains after removing one or more singular terms from a sentence. From the earlier slide: • ___ is human • ___ is bald • ___ kills … • ___ is less than … • ___ introduces … to - - - • ___ is between … and - - -

  6. Predicate Letters and Constants • We will use uppercase letters A-Z (with or without super- and subscripts) as predicates of P • We will use lowercase letters a-v (with or without subscripts) as constants of P to represent proper nouns (definite descriptions will receive a special analysis) • We will use lowercase letters w-z (with or without subscripts) as variables (to be discussed later)

  7. Interpretation in P Interpretation in P:An interpretation inP consists of 3 components: • a non-empty universe of discourse (UD) specifying the range of the variables (i.e., the things about which we’ll be talking) • an interpretation of the predicate letters, either via a translation key, or a specification of extensions • an interpretation of the constants via an assignment of objects from the UD to constants such that • every individual constant is interpreted, and • no individual constant is allowed more than one interpretation

  8. B: is bald H:  is human K:  kills  L:  is less than  B:  is between and  e: eleven l: Plato p: Plato s: Socrates t: twenty v: seven An Interpretation UD: All people and all positive integers

  9. Pronouns and Quantifiers You see, a pronoun was made to take the place of a noun ’Cause saying all those nouns over and over can really wear you down! —Albert Andreas Armadillo in “Rufus Xavier Sarsaparilla” Schoolhouse Rock

  10. Eliminable Pronouns(Pronouns of Laziness) • Socrates was human, and he killed himself • Socrates was human, and Socrates killed Socrates • Da Vinci painted the Mona Lisa and now he is considered a great artist and it is considered a masterpiece • Da Vinci painted the Mona Lisa and now Da Vinci is considered a great artist and the Mona Lisa is considered a masterpiece • Rufus Xavier Sarsaparilla found a kangaroo that followed him home and now it belongs to him • Rufus Xavier Sarsaparilla found a kangaroo that followed Rufus Xavier Sarsaparilla home, and now the kangaroo that Rufus Xavier Sarsaparilla found belongs to Rufus Xavier Sarsaparilla

  11. Ineliminable Pronouns • Any student caught cheating will have her name published and she will be expelled • Any student caught cheating will have Susie’s name published and Susie will be expelled • Any student caught cheating will have any student’s name published and any student will be expelled • Every thing is such that, if it is a student and it is caught cheating, then it will have its name published and it will be expelled

  12. Ineliminable Pronouns • Some student was caught cheating and she had her name published and she was expelled • Some student was caught cheating and Susie’s had Susie’s name published and Susie was expelled • Some student was caught cheating and some student had some student’s name published and some student was expelled • Some thing is such that, it is a student and it was caught cheating and it had its name published and it was expelled

  13. Example Quantifiers (8x) Universal x-quantifier:all (objects, things) x are such that…for all x…every (thing) x is such that… (9x) Existential x-quantifier:there exists at least one (thing) x such that…(for) some x…at least one x is such that…

  14. The Symbols of P Predicate Letters: Individual Terms: Individual Constants:a, b,…, v, a1,…, v1, a2,… Individual Variables:w, x, y, z, w1, x1, y1, z1, w2,…

  15. The Symbols of P Truth-Functional Connectives::ÆÇ!$ Quantifier Symbols:89 Punctuation Marks:( )

  16. Metavariables Metavariables: Usually ‘t’ will range over individual terms, ‘a’ over individual constants, and ‘x’ over individual variables.

  17. Expressions and Quantifiers of P Definition 5.2.1 (Expression of P). An expression of Pis any finite sequence of the symbols of P. Definition 5.2.2 (Quantifier of P). Where x ranges over individualvariables, expressions of the form (8x) are called universal quantifiers of P, whileexpressions of the form (9x) are called existential quantifiers of P.

  18. Well-Formed Formulas of P Definition 5.2.3 (Well-Formed Formula of P). Where P and Q range over expressions of P, ranges over predicate letters of P, t ranges over individual terms of P, and x ranges over individual variables of P, • Any expression of form t1,…,tn is a wff of P • If P and Q are wffs of P, then • :P is a wff of P • (PÆQ) is a wff of P • (PÇQ) is a wff of P • (P!Q) is a wff of P • (P$Q) is a wff of P • If x is an individual variable of P and P is a wff of P which i) contains at least one occurrence of x and ii) contains no x-quantifiers, then • (8x)P is a wff of P • (9x)P is a wff of P • Nothing is a wff of P unless it can be shown so by a finite number of applications of clauses 1) through 3)

  19. Syntactic Concepts Bound Variable, Free Variable:An occurrence of a variable x in a wff P is bound iff it is within the scope of an x-quantifier. An occurrence of a variable is free iff it is not bound. Open Wff:A wff of P is open iff it contains at least one free occurrence of a variable. Closed Wff, Sentence of P:A wff of P is closed iff it contains no free occurrences of variables. We also call such wffs sentences of P.

  20. Interpreting Quantifiers • Where Fx is a wff with only instances of x free: • A universally quantified wff (8x)Fx is true iff the conditionexpressed by the immediate subcomponent Fx is true of (satisfied by) every object in the UD. • An existentially quantified wff (9x)Fx is true iff the conditionexpressed by the immediate subcomponent Fx is true of (satisfied by) at least one object in the UD.

  21. B: is blue G:  is green R:  is red Y:  is yellow C:  is cracked S:  is scratched B:  is bigger than  S:  is smaller than  g: The Green Giant o: Old Yeller r: Big Red s: Sky UD: The marbles in Fred’s Collection

  22. M: is a marble S: is a Superball B: is blue G:  is green R:  is red Y:  is yellow C:  is cracked S1:  is scratched B:  belongs to  H:  bounces higher than  L:  is larger than  S:  is smaller than  G:  gives to f: Fred g: The Green Giant o: Old Yeller r: Big Red s: Susie UD: Fred, Susie, Fred’s marbles and Superballs, Susie’s marbles and Superballs

  23. A: is an accountant C:  is a cashier D:  is diligent L:  is lazy U:  is upbeat L:  likes  W:  works for  f: Fred k: Kate UD: The people in Kate’s Office

  24. E: is even O:  is odd P:  is prime G:  is greater than  L:  is less than  E:  times  is even O:  times  is odd P:  times  is prime T:  times  equals  a1: one a2: two a3: three a4: four  an: n UD: Positive Integers

  25. Simple Square of Opposition Contradictories Implies Implies

  26. Quantifiers, Conjunction, Disjunction (8x)FxÆ (8x)Gx, (8x)(FxÆGx) (8x)FxÇ (8x)Gx) (8x)(FxÇGx) (9x)FxÆ (9x)Gx( (9x)(FxÆGx) (9x)Fx Ç (9x)Gx, (9x)(FxÇGx)

  27. Modern Categorical Square of Opposition Contradictories

  28. Variations on A and O Forms

  29. Vagaries of ‘Any’

  30. Quantifiers with Overlapping Scope (9x)(9y)…There is an x and there is a y such that…There is a pair x, y such that… (8x)(8y)…For every x and for every y…For every pair x, y… (8x)(9y)…For every x there is a y such that… (9x)(8y)…There is an x such that for every y… Note: the object denoted by x is not necessarily different from y

  31. Everyone loves someone(8x)(9y)Lxy Everyone is loved by someone(8x)(9y)Lyx Someone loves everyone (9y)(8x)Lyx Someone is loved by everyone(9y)(8x)Lxy Note:4 ‘ 1, 1 — 43 ‘ 2, 2 — 3 (These are not the only models which satisfy their respective sentences. They were chosen to illustrate the above entailments/failures of entailment.) Examples of Overlapping Scopes

  32. Identity Identity:By identity we mean numerical identity—that what may appear to be distinct objects are actually one and the same thing. Object x is identical to object y iff x is y. • We do not mean exactly similar, as identical twins or triplets are exactly similar—since there are two or three of them, they are not numerically identical.

  33. Identity Sign • To express numerical identity, we introduce a new predicate letter into the symbols of P, the identity sign:  = :  is (numerically) identical to  • This predicate letter is receives a fixed interpretation for all interpretations, and so does not need to be explicitly included in any interpretation • Unlike other two-place predicates the identity sign is written with infix notation, i.e., between the individual terms: a = b a = y x = y • Rather than using a hook to negate the identity sign, we slash it: a ≠ b a ≠ y x ≠ y

  34. Identity, Definite Descriptions, and Numerical Quantification There are at least two Fs(9x)(9y)(xyÆ (FxÆFy))There is at least one x and at least one y s.t., x and y are distinct and both are F There is exactly one F(9x)(FxÆ (8y)(Fy!x = y))There is an x s.t. it is F and for any y, if y is F, then y is the same thing as x There are exactly two Fs(9x)(9y)((xyÆ (FxÆFy)) Æ (8z)(Fz! (x = zÇy = z)))There is at least one x and at least one y s.t., x and y are distinct and both are F, and for any z, if z is F, then z is either the same thing as x or the same thing as y The F is G(9x)((FxÆ (8y)(Fy!x = y)) ÆGx)There is an x s.t. it is F and for any y, if y is F, then y is the same thing as x, and x is G

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