 Another widespread idea is that part of what should distinguish logical truths is that they should be in some sense yet to be fully understood “formal”. That a logical truth is formal implies at the very least that all the sentences which are appropriate replacement instances of its logical form are logical truths too. In this context, the logical form of a sentence \(S\) is supposed to be a certain schema determined uniquely by \(S\), a schema of which \(S\) is a replacement instance, and of which sentences with the same form as \(S\) are replacement instances too. A form has at the very least the property that the expressions in it which are not schematic letters (the “logical expressions”) are widely applicable across different areas of discourse. Among people who accept the idea of formality there would be wide agreement that the forms of (1), (2) and (3) would be something like \((1')\), \((2')\) and \((3')\) respectively: