Neither Aristotelian nor Russellian rules give the exact logic of any expression of ordinary language; for ordinary language has no exact logic.
...logical validity is not a guarantee of truth.
A tautology's truth is certain, a proposition's possible, a contradiction's impossible.
All possible knowledge, then, depends on the validity of reasoning. Unless human reasoning is valid, no science can be true.
An argument can be logically valid, but unsound in that it contains a false premise and, therefore, leads to a false conclusion (e.g., Scientists are smart; smart people do not make mistakes; therefore, scientists do not make mistakes).
Propositions show what they say: tautologies and contradictions show that they say nothing.
Sentences are not as such either true or false.
