Metrical convenience and metrical preference seem to enter into a poet's choice among parens, pater, and mater. Forms of parens provide suitable and desirable endings for lines of several metres, notably the dactylic hexameter. It must be remembered that sometimes a poet may choose one word rather than another because it conveniently fits into a certain place in his line, while on other occasions he writes his line in such a way as to enable him to use the word which he desires. Perhaps the two influences counteract each other.