4.1211 Thus the proposition “fa” shows that it is about the object a, two propositions “fa” and “ga” show that they are both about the same object.
If two propositions contradict each other then their structure shows this; the same applies if one follows from the other. And so on.
In what sense is “fa” a proposition? Only according to the conventions of a concept-script. “Fa” stands in need of some interpretation, and only in a context of certain conventional understanding/interpretation does it show anything. Is LW assuming some transparent language of thought here? Is he describing how a possible concept-script might go? Is he talking nonsense? Or is he just talking about a notational system that would work well for us, given our understanding of these conventions?