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. The most frequently acknowledged types of predicative expressions are predicative adjectives (also predicate adjectives) and predicative nominals (also predicate nominals). The main trait of all predicative expressions is that they serve to express a property that is assigned to a "subject", whereby this subject is usually the clause subject, but at times it can be the clause object. A primary distinction is drawn between predicative (also predicate) and attributive expressions. Further, predicative expressions are typically not clause arguments, and they are also typically not clause adjuncts. There is hence a three-way distinction between predicative expressions, arguments, and adjuncts.
The terms predicative expression on the one hand and subject complement and object complement on the other hand overlap in meaning to a large extent.
The most widely acknowledged predicative expressions are adjectives and nominals:
The formulations "over the subject" and "over the object" indicate that the predicative expression is expressing a property that is assigned to the subject or to the object. For example, the predicative expression a thief in the last sentence serves to assign to Jill the property of being a thief. Predicative nominals over subjects are also called predicate nominatives, a term borrowed from Latin grammars and indicating the morphological case that such expressions bear (in Latin).
While the most widely acknowledged predicative expressions are adjectives and nominals, most syntactic categories can be construed as predicative expressions, e.g.
There are, however, certain categories that cannot appear as predicative expressions. Adverbs ending in -ly, for instance, cannot appear as predicative expressions, e.g.
These examples raise the following fundamental question: What characteristic of words and phrases allows or prohibits them from appearing as predicative expressions? The answer to this question is not apparent.
Predicative expressions are not attributive expressions. The distinction is illustrated best using predicative and attributive adjectives:
A given clause usually contains a single predicative expression (unless coordination is involved), but it can contain multiple words attributive expressions, e.g. The friendly man found a large snake in his damp bag.
Every real number is rational OR irrational.
Predicative expressions are typically not arguments, e.g.
The predicative expressions here are properties that are assigned to the subject, whereas the arguments cannot be construed as such properties. Predicative expressions are also typically not adjuncts, e.g.
The predicative expressions again serve to assign a property to the subject, e.g. the property of being under the bed. In contrast, the adjuncts serve to establish the situational context. One can hence acknowledge a three-way distinction between predicative expressions, arguments, and adjuncts. However, upon deeper examination, the lines between these categories become blurred and overlap can occur. For instance, in the sentence Bill arrived drunk, one can judge drunk to be both a predicative expression (because it serves to assign a property to Bill) and an adjunct (because it appears optionally in the sentence).
Predicative expressions exist in most if not all languages. In languages that have morphological case, predicative nominals typically appear in the nominative case (e.g., German and Russian) or instrumental case (e.g. Russian), although predicative expressions over objects generally bear the same case as the object. Some languages lack an equivalent of the copula be, and many languages omit the copula in some contexts or optionally (see zero copula), which means that the case marker plays a greater role since it helps distinguish predicative nominals from argument nominals. Some languages (e.g., Tabasaran and Volapük) have a separate predicative case.