Aristotle
The student answers the question the teacher left open. Aristotle’s De Interpretatione (4th century BC, Book II of the Organon) — the symbol by convention, noun and verb, the seat of truth, the square of opposition, and the sea battle. Read from the Greek.
Reading Aristotle's De Interpretatione — Words Are 'Symbols by Convention,' and Truth Lives Only in the Sentence
To the question Plato left open — is a name natural or conventional? — his student Aristotle gives a short answer: words are symbols by convention. And truth and falsity live not in words but in the 'assertion,' where words are combined. Book II of the Organon, a dense essay in fourteen chapters, read from the Greek.
'By Convention' — Aristotle's Answer to Cratylus
Into the definition of the noun Aristotle slips one phrase — 'by convention.' No name exists by nature. The cries of animals express something naturally, but they are not names. To the pair of options Plato held open, his student rules for nomos — and it becomes the mainstream for two thousand years.
Noun and Verb — the Verb 'Co-Signifies' Time
'Health' is a noun; 'is healthy' is a verb. What is the difference? For Aristotle, a verb signifies, and on top of that co-signifies 'being now' — time — and is always a sign of something 'said of another.' The two parts that build a sentence, and the puzzle of the 'is' that joins them, read from the Greek.
Truth Lives Only in the 'Assertion' — a Prayer Is Outside Logic
'It is raining' comes out true or false. 'May it rain' is neither. Aristotle takes only the sentences that carry truth — assertions (apophantikos) — as the business of logic, and sends prayers, commands and questions off to rhetoric and poetics. The unit called 'the proposition' is born here.
Affirmation and Negation, Universal and Particular — the Origin of the 'Square of Opposition'
'Every man is white' and 'no man is white' cannot both be true, but can both be false. 'Every man is white' and 'some man is not white' must have exactly one true and one false. The relations Aristotle set out in chapter 7 became the medieval 'square of opposition' — and in modern logic part of it collapses.
Will There Be a Sea Battle Tomorrow? — Future Contingents and Determinism
Is 'there will be a sea battle tomorrow' already true or false? If so, everything about tomorrow happens of necessity, and deliberation and preparation are pointless. De Interpretatione chapter 9, the most debated chapter in the history of logic. Aristotle's answer: the whole disjunction is necessary; neither disjunct is yet determined.