 Second, the definition should fix the use of the defined expression \(X\)—call this the Use criterion. This criterion is plausible, since only the definition—and nothing else—is available to guide us in the use of \(X\). There are complications here, however. What counts as a use of \(X\)? Are occurrences within the scope of ‘say’ and ‘know’ included? What about the occurrence of \(X\) within quotation contexts, and those within words, for instance, ‘Xenophanes’? The last question should receive, it is clear, the answer, “No.” But the answers to the previous questions are not so clear. There is another complication: even if we can somehow separate out genuine occurrences of \(X\), it may be that some of these occurrences are rightfully ignored by the definition. For example, a definition of quotient may leave some occurrences of the term undefined (e.g., where there is division by 0). The orthodox view is to rule such definitions as illegitimate, but the orthodoxy deserves to be challenged here. Let us leave the challenge to another occasion, however, and proceed to bypass the complications through idealization. Let us confine ourselves to ground languages that possess a clearly determined logical structure (e.g., a first-order language) and that contain no occurrences of the defined term \(X\). And let us confine ourselves to definitions that place no restrictions on legitimate occurrences of \(X\). The Use criterion now dictates then that the definition should fix the use of all expressions in the expanded language in which \(X\) occurs.