In linguistics, agreement or concord (abbreviated ) occurs when a word changes form depending on the other words to which it relates. It is an instance of inflection, and usually involves making the value of some grammatical category (such as gender or person) "agree" between varied words or parts of the sentence. For example, in Standard English, one may say I am or he is, but not "I is" or "he am". This is because English grammar requires that the verb and its subject agree in person. The pronouns I and he are first and third person respectively, as are the verb forms am and is. The verb form must be selected so that it has the same person as the subject in contrast to notional agreement, which is based on meaning. By category Agreement generally involves matching the value of some grammatical category between different constituents of a sentence (or sometimes between sentences, as in some cases where a pronoun is required to agree with its antecedent or referent). Some categories that commonly trigger grammatical agreement are noted below. Person Agreement based on grammatical person is found mostly between verb and subject. An example from English (I am vs. he is) has been given in the introduction to this article. Agreement between pronoun (or corresponding possessive adjective) and antecedent also requires the selection of the correct person. For example, if the antecedent is the first person noun phrase Mary and I, then a first person pronoun (we/us/our) is required; however, most noun phrases (the dog, my cats, Jack and Jill, etc.) are third person, and are replaced by a third person pronoun (he/she/it/they etc.). Number Agreement based on grammatical number can occur between verb and subject, as in the case of grammatical person discussed above. In fact the two categories are often conflated within verb conjugation patterns: there are specific verb forms for first person singular, second person plural and so on. Some examples: I really am (1st pers. singular) vs. We really are (1st pers. plural) The boy sings (3rd pers. singular) vs. The boys sing (3rd pers. plural) Again as with person, there is agreement in number between pronouns (or their corresponding possessives) and antecedents: The girl did her job vs. The girls did their job Agreement also occurs between nouns and their specifier and modifiers, in some situations. This is common in languages such as French