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A sentence can be viewed as expressing a proposition, something that must be true or false. The restriction of having no free variables is needed to make sure that sentences can have concrete, fixed truth values : as the free variables of a (general) formula can range over several values, the truth value of such a formula may vary.
In propositional calculus, a propositional function or a predicate is a sentence expressed in a way that would assume the value of true or false, except that within the sentence there is a variable (x) that is not defined or specified (thus being a free variable), which leaves the statement undetermined.
The notion of a predicate in traditional grammar traces back to Aristotelian logic. [2] A predicate is seen as a property that a subject has or is characterized by. A predicate is therefore an expression that can be true of something. [3] Thus, the expression "is moving" is true of anything that is moving.
A Boolean-valued function (sometimes called a predicate or a proposition) is a function of the type f : X → B, where X is an arbitrary set and where B is a Boolean domain, i.e. a generic two-element set, (for example B = {0, 1}), whose elements are interpreted as logical values, for example, 0 = false and 1 = true, i.e., a single bit of information.
[2] Example. In a given propositional logic, a formula can be defined as follows: Every propositional variable is a formula. Given a formula X, the negation ¬X is a formula. Given two formulas X and Y, and a binary connective b (such as the logical conjunction ∧), the expression (X b Y) is a formula. (Note the parentheses.)
A predicative expression (or just predicative) is part of a clause predicate, and is an expression that typically follows a copula or linking verb, e.g. be, seem, appear, or that appears as a second complement of a certain type of verb, e.g. call, make, name, etc. [1] The most frequently acknowledged types of predicative expressions are predicative adjectives (also predicate adjectives) and ...
However, we cannot do the same with the predicate. That is, the following expression: ∃P P(b) is not a sentence of first-order logic, but this is a legitimate sentence of second-order logic. Here, P is a predicate variable and is semantically a set of individuals. [1] As a result, second-order logic has greater expressive power than first ...
Control predicates semantically select their arguments, as stated above. Raising predicates, in contrast, do not semantically select (at least) one of their dependents. The contrast is evident with the so-called raising-to-object verbs (=ECM-verbs) such as believe, expect, want, and prove. Compare the following a- and b-sentences: a.