De dicto

Item, dato quod ly ‘hominis’ potest distribui similariter et rectus tunc esset distinguenda sicut ista “omnis homo qui est albus currit” secundum compositionen et divisionem, ita quod ly ‘hominis asinus’ in sensu compositionis distribuetur et in sensu divisionis non. Dicetur quod hoc bene potest esse. Contra, dato hoc tunc in sensu compositionis bene potest fieri descensus sic “istius hominis ille asinus currit” et sic de aliis ut patet in aliis, et non est dicere quod ista “omnis homo qui est albus currit” est distinguenda propter compositionem expressam ...

In scholastic logic, the de dicto sense of a proposition is one where the subject is a dictum, i.e. something that is said or stated, and the predicate is some qualifier such as 'is necessary' or 'is known'. For example, the proposition 'Socrates necessarily runs' can be interpreted de dicto as predicating necessity of the dictum 'that Socrates runs' or 'Socrates's running'. Thus 'it is necessary that Socrates runs'. A de re sense is where the subject is the literal subject of the proposition (i.e. 'Socrates') and the predicate is qualified by the mode. For example 'Socrates necessarily runs' can be interpreted de re as stating that there is some necessity of running belong to Socrates himself.

Another example is the apparently contradictory 'A standing man can sit’. The de dicto or composite sense is that the proposition 'a standing man is sitting' is possibly true, in which sense it is contradictory and false. However, the de re or divided sense is that a man who is now sitting can possibly sit (i.e. in the future), and in this sense it is true.

Examples

The anonymous author of Summa totius logicae (Tract. 6, chapter 11) writes

it should be noted that some modal propositions are de dicto, such as "that Socrates runs is necessary", namely those in which the dictum [i.e. the clause 'that Socrates runs'] is the subject and the mode [i.e. 'is necessary'] is the predicate, and these are truly modals, for the mode here determines the verb by reason of composition, as was said above. And some are modals de re, namely in which the mode is interposed in the dictum, e.g. "Socrates necessarily is running", for the sense is not now that the dictum is necessary, namely 'that Socrates runs', but the sense of it is that in Socrates there is 'necessity towards running'.

In Summa Theologiae [1], Thomas Aquinas says that the proposition 'Everything known by God must necessarily be" has distinct senses, namely de re and de dicto. If de re, it is false, for it would mean that everything which God knows is necessary. But if understood de dicto, it means that, necessarily, everything known by God is the case.

The de dicto sense was sometimes called the sense of composition, the de re sense, the sense of division. For example, in Summa logicae, Book II chapter 9, Ockham says that in the 'sense of composition' (i.e. de dicto), the proposition 'it is necessary that every man is an animal', it is denoted that the mode 'necessary' is predicated of the proposition 'every man is an animal'. But in the 'sense of division' (i.e. de re) it means that it is true every man that, of necessity, he or she is an animal. He points out that (in Latin at least) the ambiguity of sense can be resolved by grammar. If subject combines the terms of the dictum in the accusative case with the verb in the infinitive mood (omnem hominem esse animal est necessarium) then it is a de dicto proposition. The English equivalent would be the awkward 'every man's being an animal is necessary'. If the subject is in the nominative case, and if the verb or predicate is modified by the mode (e.g. 'is of necessity'), then it is a de re proposition. He points out that the mode can also involve other qualifiers such as 'is known'.

See also

• Dici de omni

Links

• Modalities in Thirteenth-Century Logical Treatises in the SEP written by Simo Knuuttila.