1. Formal logic has been described as the science of deduction.

2. In formal logic: Modal logic …a republic”—that are not (Contingently true propositions)

3. In Łukasiewicz's 1951 book, Aristotle's Syllogistic from the Standpoint of Modern Formal Logic, he mentions that the principle of his notation was to write the functors before the arguments to avoid brackets and that he had employed his notation in his logical papers since 1929.