Aristotle "says that `on the subject of reasoning' he `had nothing else on an earlier date to speak about'" (Bochenski, 1951). However, Plato reports that syntax was thought of before him, by Prodikos of Keos, who was concerned by the right use of words. Logic seems to have emerged from dialectics, the earlier philosophers used concepts like reductio ad absurdum as rule when discussing, but never understood its logical implications. Even Plato had difficulties with logic. Although he had the idea of constructing a system for deduction, he was never able to construct one. Instead, he relied on his dialectic, which was a confusion between different sciences and methods (Bochenski, 1951). Plato thought that deduction would simply follow from premises, so he focused on having good premises so that the conclusion would follow. Later on, Plato realised that a method for obtaining the conclusion would be beneficial. Plato never obtained such a method, but his best attempt was published in his book Sophist, where he introduced his division method (Rose, 1968).

Analytics and the Organon:
What we call today Aristotelian logic, Aristotle himself would have labelled analytics. The term logic he reserved to mean dialectics. Most of Aristotle's work is probably not authentic, since it was most likely edited by students and later lecturers. The logical works of Aristotle were compiled into six books at about the time of Christ:

  1. Categories
  2. On Interpretation
  3. Prior Analytics
  4. Posterior Analytics
  5. Topics
  6. On Sophistical Refutations

The order of the books (or the teachings from which they are composed) is not certain, but this list was derived from analysis of Aristotle's writings. There is one volume of Aristotle's concerning logic not found in the Organon, namely the fourth book of Metaphysics. (Bochenski, 1951).

Modal logic:
Aristotle is also the creator of syllogisms with modalities (modal logic). The word modal refers to the word `modes', explaining the fact that modal logic deals with the modes of truth. Aristotle introduced the qualification of necessarily and possibly premises. He constructed a logic which helped in the evaluation of truth but which was very difficult to interpret. (Rose, 1968).