The verifiability criterion says that a sentence is significant if and only if it has some relation to the observation. The message Ayer is trying to establish is the meaning of a sentence by linking it to a set of observation sentences and does not require observations to be made. All that is needed is that in principle we can make these observations. Ayer defines meaningfulness in terms of what he calls strong verifiability and defines meaningfulness in terms of conclusive verification or conclusive falsification. The first attempt to define meaningfulness in terms of strong verification is to say that a sentence is significant if and only if it is definitively verifiable. A second attempt is to say that a sentence is significant if it is definitively falsifiable. Ayer responds to this suggestion by arguing that no generalization can be conclusively verified or falsified by experience. Ayer's definition of verifiability says: “We call an experiential proposition a proposition that records an actual or possible observation. Then we can say that it is the mark of a genuine factual proposition, not that it should be equivalent to an experiential proposition, or to any finite number of experiential propositions, but simply that some experiential propositions can be deduced from it together with some other propositions. premises without being deducible only from those other premises." (pp. 38-39) Claims that a sentence has empirical concerns, and therefore is significant, if added to a set of propositions it changes, the observation sentences follow from that stock of propositions .Falsifiability, as defined by the philosopher Karl Popper, defines the intrinsic testability of any scientific hypothesis... middle of paper...' in short, falsifiability does not seem sufficiently restrictive, admitting as "scientific" some hypotheses that are not appear to justify such a classification.Another example is a hypothesis such as proton decay which, strictly speaking, cannot be falsified because no matter how long the decay has not been observed, it remains possible that it could still occur suppose that P and Q are falsifiable theories (in the Popperian sense). Then it seems to me that "P and Q" is a falsifiable theory. However, it seems to me that, even if P and Q are falsifiable theories, the sentence "if P, then Q" isn't necessarily. This is a bit strange, because for example the statement "if P and Q, then Q" is a logical tautology. So it's clearly true. But Popper seems to suggest that, for most choices of P and Q, this statement is unfalsifiable and therefore unscientific..