Originally Posted by
evolo
A sentence of this form- 'a is b' (is being the key word), there are only two truth values that can be assigned to the sentence. These being, logically true and logically false. But it is impossible to determine which one fits the particular sentence because it is a simple declaritive sentence which has no logical properties that can determine the truth of itself. 'The sky is blue' is a sentence in the same form. But you cannot say that this is logically true, likewise, you cannot say that this is logically false (don't try to argue that, you will lose). These sentences cannot be defined in virtue of their logical form; their truths rely on empirical oberservations. The truth property of a sentence, 'P', in the form 'a is b' cannot be recovered using logic.
'This sentence is false' is an interesting idea because it cannot be defined by logic in light of its improper form but rather it can only be defined by its content (which relies on empirical evidence). The interesting part is that this particular sentence itself calls upon logic to determine its truth property but logic has no authority to determine its truth property.
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