In obedience to the feeling of reality, we shall insist that, in the analysis of propositions, nothing "unreal" is to be admitted. But, after all, if there is nothing unreal, how, it may be asked, could we admit anything unreal? The reply is that, in dealing with propositions, we are dealing in the first instance with symbols, and if we attribute significance to groups of symbols which have no significance, we shall fall into the error of admitting unrealities, in the only sense in which this is possible, namely, as objects described. In the proposition "I met a unicorn," the whole four words together make a significant proposition, and the word "unicorn" by itself is significant, in just the same sense as the word "man." But the two words "a unicorn" do not form a subordinate group having a meaning of its own. Thus if we falsely attribute meaning to these two words, we find ourselves saddled with "a unicorn," and with the problem how there can be such a thing in a world where there are no unicorns. "A unicorn" is an indefinite description which describes nothing. It is not an indefinite description which describes something unreal. Such a proposition as " is unreal" only has meaning when "" is a description, definite or indefinite; in that case the proposition will be true if "" is a description which describes nothing. But whether the description "" describes something or describes nothing, it is in any case not a constituent of the proposition in which it occurs; like "a unicorn" just now, it is not a subordinate group having a meaning of its own. All this results from the fact that, when "" is a description, " is unreal" or " does not exist" is not nonsense, but is always significant and sometimes true. [Pg 170] We may now proceed to define generally the meaning of propositions which contain ambiguous descriptions. Suppose we wish to make some statement about "a so-and-so," where "so-and-so's" are those objects that have a certain property , i.e. those objects for which the propositional function is true. (E.g. if we take "a man" as our instance of "a so-and-so," will be " is human.") Let us now wish to assert the property of "a so-and-so," i.e. we wish to assert that "a so-and-so" has that property which has when is true. (E.g. in the case of "I met a man," will be "I met .") Now the proposition that "a so-and-so" has the property is not a proposition of the form "." If it were, "a so-and-so" would have to be identical with for a suitable ; and although (in a sense) this may be true in some cases, it is certainly not true in such a case as "a unicorn." It is just this fact, that the statement that a so-and-so has the property is not of the form , which makes it possible for "a so-and-so" to be, in a certain clearly definable sense, "unreal." The definition is as follows:— The statement that "an object having the property has the property " means: "The joint assertion of and is not always false."