 Though Frege essentially had a second-order logic in Gg, his rules of inference don’t look as familiar, or as simple, as MP and GEN. The reason is that Frege’s rules of inference govern not only his graphical notation for molecular and quantified formulas, but also his special purpose symbols, such as certain lowercase letters used as placeholders, certain Gothic letters and letters used as bound variables, and various other signs of his system we have not yet mentioned. Since Frege’s notation for rules of inference will play no role in the discussion that follows, we shall again simplify our task by not describing it further.