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2250 (23)
Lecture

3 Pages
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School
Buffalo State College
Department
Philosophy
Course
2250
Professor
James Hildebrand
Semester
Spring

Description
Common Mistakes and Correct Solutions for Monday’s Assignment Common mistakes: 1. 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. You see this on the truth table. 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. The value is always known. 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, the column of truth values under its main connective contains at least one T and at least one F. This is what differentiates it from t-f true sentences (which are true on every tva and on every line of the truth table) and from t-f false sentences (which are false on every tva and on every line of the truth table). 2. Confusing truth on a truth value assignment with truth-functional truth. To say that a sentence is truth functionally true is to say that it is true on every truth value assignment, not just that it is true on some truth value assignment (or just “true” as some people ambiguously put it). On the truth table, there will be a column of only T’s under its main connective. 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. For this reason, you should never say that a sentence is just true or just false. No sentence of SL is ever just true or just false. They are either true on some truth value assignment or false on that truth value assignment, or true on all truth value assignments or false on all truth value assignments. 3. Giving arguments where examples are called for and examples where arguments are called for. Whenever you are trying to show that something does not have to be the case, an example is called for. When you are trying to show that something does have to be the case, an argument appealing to the semantic rules and definitions is called for. Since 4f, 4j, and 5b are all false, examples are called for. The other questions all call for arguments. 4. Only doing half the job. Question 4h does not just ask you to prove that if a sentence is t-f indeterminate then its negation is t-f indeterminate, but the converse as well, that if a negation is t-f indeterminate then its immediate component is t-f indeterminate as well. 5. Trying to use truth tables to answer questions about metavariables. The metavariables, P and Q, stand for arbitrarily complex sentences of SL. Consequently there is no way of telling how many lines there are on their truth tables. If the sentences are t-f indeterminate, there is also no way of telling how the T’s and F’s are distributed under their main connectives. 6. At
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