  From this passage we may infer that it was a peculiarity of all past true propositions that they cannot change their truth-value to falsehood; and that because of this they are necessary. This suggests that the past true propositions at issue do not include all propositions in the past tense, but that they were those propositions which correspond to some past state or event. For instance, the true past proposition ‘I went to Athens’ corresponds to the event of my having gone to Athens. It can never become false, once it is true. Assume that I went to Athens last month. Then the proposition ‘I went to Athens’ is not only true now, it will also be true tomorrow, the day after, and in fact always from now on. The truth of the proposition is based on the fact that there has been a case of my going to Athens, and — whatever happens from now on — this cannot unhappen. (One can bring out this feature more clearly by reformulating the proposition as ‘It has been the case that I went to Athens’). On the other hand, the proposition ‘You have not been to Athens’ does not correspond to a past state or event. Suppose that up to now you never went to Athens. Then the proposition is true now. Now suppose in addition that you will go to Athens next week. After you have gone there, the proposition ‘You have not been to Athens’ is no longer true. Hence it is not necessary now. (This proposition cannot be correctly paraphrased as ‘It has been the case that you were not in Athens’). We may hence reformulate statement (I) as