logic terminology

Question 1

logical equivalence =

Answer 1

two sentences are logically equivalent iff they are true under the exact same interpretation of the subject specific vocabulary.

Question 2

contingent sentences =

Answer 2

a sentence is contingent iff it is true under some interpretations of the subject specific vocabulary and false under others
mix of T’s and F’s in the main column of the truth table - everything that isn’t a tautology or a contradiction is contingent

Question 3

tautology =

Answer 3

only T’s in the main column of the truth table

Question 4

contradiction =

Answer 4

only F’s in the main column of the truth table

Question 5

theorem for contingency =

Answer 5

P is contingent iff ¬P is also contingent and vice versa

Question 6

satisfiability =

Answer 6

a set of sentences is satisfiable iff there is at least one interpretation of the subject specific vocabulary under which all sentences in the set are true.