The modality of judgments, which engaged the attention of Aristotle and his immediate pupils so much, was likewise treated by the Stoics at considerable length; but of this branch of enquiry so much only is known to us as concerns possible and necessary judgments, and it is the outcome chiefly of the contest between Chrysippus and the Megarian Diodorus. [223] It is in itself of no great value. By the Stoics, nevertheless, great value was attached to it, in the hope of escaping thereby the difficulties which necessarily result from their views on freedom and necessity. [224] [(b) Inference.] In their theory of illation, [225] to which the Stoics attached special value, and on which they greatly prided themselves, [226] chief attention was paid to hypothetical and disjunctive inferences. [227] In regard to these forms of inference, the rules they laid down are well known: [228] and from these forms they invariably take their examples, even when treating of inference [(α) Hypothetical inference the original form.] in general. [229] According to Alexander, [230] the hypothetical and disjunctive forms are held to be the only regular forms of inference; [231] the categorical form is considered correct in point of fact, but defective in syllogistic form. [232] In hypothetical inferences a distinction was also made between such as are connected and such as are disconnected. [233] In connected inferences the Stoics look principally at the greater or less accuracy of expression, [234] and partly at the difference between correctness of form and truth of matter. [235] They also remark that true conclusions do not always extend the field of knowledge; and that those which do frequently depend on reasons conclusive for the individual, but not on proofs universally acknowledged. [236] The main point, however, to be considered in dividing inferences is their [(β) The five simple forms of hypothetical inference.] logical form. There are, according to Chrysippus, [237] who herein adopted the division of Theophrastus, five original forms of hypothetical inference, the accuracy of which is beyond dispute, and to which all other forms of inference may be referred and by which they may be tested. [238] Yet even among these five, importance is attached to some in which the same sentence is repeated tautologically in the form of a conclusion, [239] which proves how mechanical and barren must have been the formalism with which the Stoic logic abounds. [(γ) Composite forms of inference.]