The most distinctive doctrine of the logical positivists was that for any sentence to be cognitively meaningful it must express a statement that is either analytic or empirically verifiable. It was allowed that sentences may have "emotive," "imperative," and other kinds of meaning (for example, "What a lovely present!" or "Bring me a glass of water!") even when they have no cognitive meaning, that is, when they do not express anything that could be true or false, or a possible subject of knowledge. But—leaving aside sentences expressing analytic statements—for a sentence to have "cognitive," "factual," "descriptive," or "literal" meaning (for example, "The sun is 93 million miles from the earth") it was held that it must express a statement that could, at least in principle, be shown to be true or false, or to some degree probable, by reference to empirical observations. The iconoclasm of...