text: Derek Parfit melded this number of ethical theories into one in his 2011 book
full_question: Derek Parfit melded this number of ethical theories into one in his 2011 book On What Matters. A theory about knowledge opposed in a 1966 paper by Edmund Gettier has this many criteria for establishing that "S knows P". In an allegory about Chinese philosophies, this many people taste vinegar and all have different reactions. The soul is divisible into this many parts according to Plato's Republic. The "positive (*) stage" comes last in a model of this many societal stages proposed by Auguste Comte. Hegel's dialectic is often erroneously divided into this many stages. For 10 points, give this number of Critiques written by Immanuel Kant, also the number of propositions in a classical syllogism that has a major premise, a minor premise, and a conclusion.
first_sentence: Derek Parfit melded this number of ethical theories into one in his 2011 book
raw_answer: three [or 3] 