The first is a purely verbal point. When Popper contrasts acceptability, or degree of corroboration, with probability, he does not always make clear that he refers only to probability in a technical sense in which it is a measure of chance. The second point is of more importance, and it is this the author wish to discuss. When Popper connects the high acceptability of a successful scientific hypothesis with its low absolute logical probability, he thinks that what he says marks a fundamental difference between laws of nature and laws of logic. In his Tractatus, Wittgenstein introduces the notion of probability by saying that the probability which one proposition gives to another is the ratio of the number of their common truth-grounds to the number of the truth-grounds of the first. But there is nothing in all this to show that the word 'necessity' has different meanings in the phrases 'natural necessity' and 'logical necessity.'.