The Organon is the standard collection of Aristotle's six works on logic. The name Organon was given by Aristotle's followers, the Peripatetics. They are as follows: The Isagoge or "Introduction" to Aristotle's "Categories," written by Porphyry. The work includes the highly influential hierarchical classification of genera and species from substance in general down to individuals, known as the Tree of Porphyry, and an introduction which mentions the problem of universals. The Categories (Latin: Categoriae) introduces Aristotle's 10-fold classification of that which exists: substance, quantity, quality, relation, place, time, situation, condition, action, and passion. On Interpretation (Latin: De Interpretatione, Greek Perihermenias) introduces Aristotle's conception of proposition and judgment, and the various relations between affirmative, negative, universal, and particular propositions. Aristotle discusses the square of opposition or square of Apuleius in Chapter 7 and its appendix Chapter 8. Chapter 9 deals with the problem of future contingents. The Prior Analytics (Latin: Analytica Priora) introduces his syllogistic method (see term logic), argues for its correctness, and discusses inductive inference. The Posterior Analytics (Latin: Analytica Posteriora) deals with demonstration, definition, and scientific knowledge. The Topics (Latin: Topica) treats issues in constructing valid arguments, and inference that is probable, rather than certain. It is in this treatise that Aristotle mentions the Predicables, later discussed by Porphyry and the scholastic logicians. The Sophistical Refutations (Latin: De Sophisticis Elenchis) gives a treatment of logical fallacies, and provides a key link to Aristotle's work on rhetoric