2250 Lecture : 3.2 answers.pdf
5 Feb 2013
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Common mistakes: misunderstanding the concept of truth functional indeterminacy. To say that a sentence is t-f indeterminate is not to say that its truth value is unknown. The truth value of every sentence of sl is always exactly one or the other of t or f, and which it is, is always known. There are no blank spaces on the truth table. On every line of every truth table, every sentence gets either a t or an f assigned to its main connective. What makes a sentence t-f indeterminate is not that it has an unknown truth value, but that it has different truth values on different truth value assignments. On the truth table, there will be a column of only. From the fact that there is one truth value assignment that assigns a t to the sentence, you cannot infer that the sentence is truth functionally true, but just that it is true on that one truth value assignment.
