Phi 270
Fall 2013
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Phi 270 F13 test 4

F13 test 4 topics

The following are the topics to be covered. The proportion of the test covering each will approximate the proportion of the classes so far that have been devoted to that topic. Your homework and the collection of old tests will provide specific examples of the kinds of questions I might ask.

Analysis. Be ready to handle any of the key issues discussed in class—for example,

the proper analysis of every, no, and only (see §7.2.2),

how to incorporate bounds on complementary generalizations (see §7.2.3),

ways of handling compound quantifier phrases (such as only cats and dogs, see §7.3.2),

the distinction between every and any (see §§7.3.3 and 7.4.2),

how to analyze multiple quantifier phrases with overlapping scope (see §7.4.1).

You should be able restate your analysis using unrestricted quantifiers (see §7.2.1), but you will not need to present it in English notation.

Synthesis. You may be given a symbolic form and an interpretation of its non-logical vocabulary and asked to express the sentence in English. Remember that the distinction between every and any can be important here, too.

Derivations. Be able to construct derivations to show that entailments hold and to show that they fail. I may tell you in advance whether an entailment holds or leave it to you to check that using derivations. If a derivation fails, you may be asked to present a counterexample; that will involve describing a structure, which may be done either with a diagram or with tables. You will not be responsible for the rules introduced in §7.8.1.


F13 test 4 questions

Analyze the sentences below in as much detail as possible, providing a key to the non-logical vocabulary you use. Also restate your analyses using unrestricted quantifiers.

1.

Every recommended book was worth reading, and Al reads everything.

answer
2.

The movie wasn’t recommended by anyone who Al spoke to.

answer
3.

No traveller has been to every city on the planet.

answer

Synthesize an English sentence that has the following logical form; that is, devise a sentence that would have the following analysis:

4.

¬ (∀x: Ax ∧ ¬ Hx) ¬ Pxa

A: [ _ is an activity]; H: [ _ is healthy]; P: [ _ was popular among _’s friends]; a: Al

answer

Use derivations to show that the following entailments hold. You may use any rules.

5.

∀x (Fx → (Gx ∧ Hx)) ⊨ ∀x (Fx → Hx)

answer
6.

∀x ∀y Rxy ⊨ ∀x Rax

answer

Use a derivation to show that the following claim of entailment fails, and present a counterexample that lurks in an open gap. You may present the counterexample either by a diagram or by tables.

7.

∀x Rax ⊨ ∀x ∀y Rxy

answer

F13 test 4 answers

1.

Every recommended book was worth reading, and Al reads everything

Every recommended book was worth reading
∧ Al reads everything

Every recommended book is s.t. (it was worth reading)
∧ everything is s.t. (Al reads it)

(∀x: x is a recommended book) x was worth reading
∧ ∀y Al reads y

(∀x: x is a book ∧ x was recommended) x was worth reading
∧ ∀y Al reads y

(∀x: Bx ∧ Rx) Wx ∧ ∀y Day
∀x ((Bx ∧ Rx) → Wx) ∧ ∀y Day

B: [ _ is a book]; D: [ _ reads _ ]; R: [ _ was recommended]; W: [ _ was worth reading]; a: Al

(∀x: Bx ∧ Rx) Wx ∧ ∀x Dax is also correct; but it is wrong to use a restriction y is a thing on the second generalization

2.

The movie wasn’t recommended by anyone who Al spoke to

Everyone who Al spoke to is s.t. (the movie wasn’t recommended by him or her)

(∀x: x is a person who Al spoke to) the movie wasn’t recommended by x

(∀x: x is a person ∧ Al spoke to x) ¬ the movie was recommended by x

(∀x: Px ∧ Sax) ¬ Rmx
∀x ((Px ∧ Sax) → ¬ Rmx)

P: [ _ is a person]; S: [ _ spoke to _ ]; R: [ _ was recommended by _ ]; a: Al; m: the movie

¬ (∀x: Px ∧ Sax) Rmx wrong; it is the analysis of The movie wasn’t recommended by everyone who Al spoke to

3.

No traveller has been to every city on the planet

No traveller is s.t. (he or she has been to every city on the planet)

(∀x: x is a traveller) ¬ x has been to every city on the planet

(∀x: x is a traveller) ¬ every city on the planet is s.t. (x has been to it)

(∀x: x is a traveller) ¬ (∀y: y is a city on the planet) x has been to y

(∀x: x is a traveller) ¬ (∀y: y is a city ∧ y is on the planet) x has been to y

(∀x: Tx) ¬ (∀y: Cy ∧ Nyp) Bxy
∀x (Tx → ¬ ∀y((Cy ∧ Nyp) → Bxy))

T: [ _ is a traveller]; C: [ _ is a city]; N: [ _ is on _ ]; B: [ _ has been to _ ]; p: the planet

Some incorrect answers: (∀x: Tx) (∀y: Cy ∧ Nyp) ¬ Bxy and (∀y: Cy ∧ Nyp) (∀x: Tx) ¬ Bxy would say No traveller has been to any city on the planet; ¬ (∀x: Tx) (∀y: Cy ∧ Nyp) Bxy would say Not every traveller has been to every city on the planet; (∀x: ¬ Tx) (∀y: Cy ∧ Nyp) Bxy would say Every non-traveller has been to every city on the planet; and (∀y: Cy ∧ Nyp) ¬ (∀x: Tx) Bxy would say No city on the planet has had every traveler visit it

4.

¬ (∀x: Ax ∧ ¬ Hx) ¬ Pxa with A: [ _ is an activity]; H: [ _ is healthy]; P: [ _ was popular among _’s friends]; a: Al

¬ (∀x: x is an activity ∧ ¬ x is healthy) ¬ was popular among Al’s friends

¬ (∀x: x is an activity ∧ x is unhealthy) ¬ was popular among Al’s friends

¬ (∀x: x is an unhealthy activity) was unpopular among Al’s friends

¬ every unhealthy activity is s.t. (it was unpopular among Al’s friends)

¬ every unhealthy activity was unpopular among Al’s friends

Not every unhealthy activity was unpopular among Al’s friends

Also correct: Not every unhealthy activity failed to be popular among Al’s friends; Not only healthy activities were popular among Al’s friends; It’s false that no unhealthy activity was popular among Al’s friends

5.
│∀x (Fx → (Gx ∧ Hx))a:3
├─
│ⓐ
│││Fa(4)
││├─
3 UI│││Fa → (Ga ∧ Ha)4
4 MPP│││Ga ∧ Ha5
5 Ext│││Ga
5 Ext│││Ha(6)
│││●
││├─
6 QED│││Ha2
│├─
2 CP││Fa → Ha1
├─
1 UG│∀x (Fx → Hx)
6.
│∀x ∀y Rxya:2
├─
│ⓑ
2 UI││∀y Rayb:3
3 UI││Rab(4)
││●
│├─
4 QED││Rab1
├─
1 UG│∀x Rax
7.
│∀x Raxa:3, b:4, c:5
├─
│ⓑ
││ⓒ
3 UI│││Raa
4 UI│││Rab
5 UI│││Rac
││││¬ Rbc
│││├─
││││○ ¬ Rbc, Rac, Rab, Raa ⊭ ⊥
│││├─
││││⊥6
││├─
6 IP│││Rbc2
│├─
2 UG││∀y Rby1
├─
1 UG│∀x ∀y Rxy

Only one of the following styles of presentation was needed:

Counterexample presented by a diagram

Counterexample presented by tables

abc
123
R123
1TTT
2FFF
3FFF