Could go either way. Sometimes I'll just think of a melody line while playing a chord progression to some known song. For example, that happened one time when I was playing the chords to a Gordon Lightfoot song, "Changes." I just "heard a different melody line that fit the same chords and later added lyrics. On other occasions, I've thought of a lyric or poetic phrasing and later composed music around that. Folk music, blues, jazz (dixieland through swing and west coast ) have all interested me and influenced my efforts.