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Full Idea
First-order logic is distinguished by generalizations (quantification) only over objects: second-order logic admits generalizations or quantification over properties or kinds of objects, and over relations between them, and functions defined over them.
Gist of Idea
First-order logic concerns objects; second-order adds properties, kinds, relations and functions
Source
Michael Dummett (The Philosophy of Mathematics [1998], 3.1)
Book Ref
'Philosophy 2: further through the subject', ed/tr. Grayling,A.C. [OUP 1998], p.134
A Reaction
Second-order logic was introduced by Frege, but is (interestingly) rejected by Quine, because of the ontological commitments involved. I remain unconvinced that quantification entails ontological commitment, so I'm happy.
10705 | Putting a predicate letter in a quantifier is to make it the name of an entity [Quine] |
9186 | First-order logic concerns objects; second-order adds properties, kinds, relations and functions [Dummett] |
13671 | Second-order quantifiers are just like plural quantifiers in ordinary language, with no extra ontology [Boolos, by Shapiro] |
10569 | If you ask what F the second-order quantifier quantifies over, you treat it as first-order [Fine,K] |
10290 | Second-order variables also range over properties, sets, relations or functions [Shapiro] |
10175 | Three types of variable in second-order logic, for objects, functions, and predicates/sets [Reck/Price] |
10978 | In second-order logic the higher-order variables range over all the properties of the objects [Read] |
5740 | Second-order logic needs second-order variables and quantification into predicate position [Melia] |
13453 | Perhaps second-order quantifications cover concepts of objects, rather than plain objects [Rayo/Uzquiano] |
18761 | Second-order variables need to range over more than collections of first-order objects [McGee] |
18763 | Basic variables in second-order logic are taken to range over subsets of the individuals [Anderson,CA] |