DEMONSTRATION AND SELF-EVIDENCE 7 



distributed at least once) are canons of valid or consistent 

 discourse. Demonstration, on the other hand, while pre- 

 supposing validity, is defined in terms of scientific force. And 

 there are general rules, able to be determined apart from any- 

 particular scientific subject, which must be followed if a syllo- 

 gism is to be demonstration (e. g., the premises must be 

 necessarily true) , and even more determinate general rules 

 which must be followed if the demonstration is to be of a 

 certain type (e. g., explanatory demonstration must have a 

 middle term which is related to the scientific subject as its 

 real definition) . These rules, while quite clearly remaining of 

 a general logical character (i. e., open to contraction in the 

 face of special scientific subject matter, but not yet con- 

 tracted ) are canons of properly scientific, and not simply con- 

 sistent, discourse. Rules such as these are proper to material 

 logic, while the rules of merely consistent discourse are rules 

 of formal logic. There are reasons which explain why formal 

 logic is sometimes confused with the whole of logic and why 

 material logic is sometimes confused with particular scientific 

 methodology.* But these reasons only help to excuse the man 



* The formal subject of the science of logic is the second intention. Second inten- 

 tions are logical forms or relations of the reason which accrue to objects (first 

 intentions) precisely as known. Some second intentions accrue to an object 

 properly in virtue of its mode of signifying (e. g., predicate, middle term, and 

 syllogism) . Others accrue directly in virtue of the intelligible content of the object 

 (e. g., species, immediate, and demonstration) . The former are second intentions in 

 formal logic, and they set the demands for valid discourse. The latter are second 

 intentions in Tnaterial logic, and these set the demands for scientific discourse. 

 Although St. Thomas explicitly distinguishes between formal and material logic 

 only on the level of the logic of the third operaton (cf., In I Post. Anal., prooem., 

 nn. 5-6) , the distinction makes sense also on the levels of the first and second 

 operations, as the examples above illustrate. [Cf., Simon, Yves, " Foreword," The 

 Material Logic oj John of St. Thomas, translated by Yves Simon, John Glanville, 

 and G. Donald Hollenhorst (Chicago: Chicago University Press, 1955), pp. ix-xxiii.] 

 The subject matter for logical theory is always the second intention, and never 

 directly the first intention to which the second intention accrues. Thus, there is a 

 sense in which logic is only formal (investigating logical forms) and never material 

 (discussing the mtelligible content of first intentions, which is the matter of dis- 

 course) . And even apart from this, it is clear that second intentions in material 

 logic are more proximately connected with the intelligible content of first intentions 



