chapter  21
“If” and “Imply”, A Reply to Mr. MacColl [1908]
Pages 4

Mr. MacColl, in an important series of papers,† has contended for the view that implication and propositions are more fundamental than inclusion and classes; and in this opinion I agree with him. But he does not appear to me to realize adequately the distinction between genuine propositions and such as contain a real 〈free〉 variable: thus he is led to speak of propositions as sometimes true and sometimes false, which of course is impossible with a genuine proposition.