Homework on §1.2—assigned Mon 8/31 and due Wed 9/2
(i) Give your own example of four non-equivalent sentences that make up a “square of opposition”—i.e., two mutually exclusive sentences each of implies one of a pair of jointly exhaustive sentences and is contradictory to the other:
| sentence 3 ▿ sentence 4 | |
| sentence 1 ⊨ sentence 3 | sentence 2 ⊨ sentence 4 |
| sentence 1 ⋈ sentence 4 | sentence 2 ⋈ sentence 3 |
| sentence 1 ▵ sentence 2 | |
(The bottom three relations are enough to get you all the rest.)
(ii) Pick one pair of sentences from the square and briefly describe a possible world in which they have different truth values.