Symbols are not what they seem to be. In “a R b”, “R” looks like a substantive, but is not one. What symbolizes in “a R b” is that R occurs between a and b. Hence “R” is not the indefinable in “a R b”. Similarly in “φx”, “φ” looks like a substantive but is not one; in “~p”, “~” looks like “φ” but is not like it. This is the first thing that indicates that there may not be logical constants. A reason against them is the generality of logic: logic cannot treat a special set of things.