There are three concords in simple sentences:
1. A finite verb agrees with its subject in number and person ( cross949).
2. A word in apposition with another word agrees with it in case ( cross976).
3. An adjective agrees with its substantive in gender, number, and case ( cross1020).
(For the concord of relative pronouns, see cross2501.)
Apparent violation of the concords is to be explained either by
a. Construction according to sense, where the agreement is with the real gender or number (e.g. 949 a, 950-953, 958, 996, 997, 1013, 1044, 1050, 1055 a, 1058 b); or by
b. Attraction, when a word does not have its natural construction because of the influence of some other word or words in its clause (e.g. 1060 ff., 1239, 1978, 2465, 2502, 2522 ff.). This principle extends to moods and tenses ( cross2183 ff.).
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].