"thematic line" is correct and usable in written English.
It can be used when discussing a narrative, such as a story, in which a theme or set of ideas is followed throughout. For example, "The author of the novel follows a thematic line of loyalty and betrayal throughout the story."
Yet, amid the spiraling flights and blasts of jerky chords, a halting thematic line threads through the textures.
In "Portrait of Himself," a searching, restless thematic line threads through the overall orchestral haze of pungent cluster chords.
For all the darting phrases and layered textures, a clear thematic line runs through the music, almost like a narrative voice.
As an encore he played a short piece by the Hungarian master Gyorgy Kurtag called "Faith," in which a somberly pensive thematic line goes through passing fits on its way to a resigned conclusion.
Yet, if keening over the Old South had been the movie's sole thematic line, "Gone with the Wind," as Molly Haskell notes, would have been forgotten, along with many mossy plantation novels and films of the period.
But then there's the thematic line as well, and that doesn't keep exactly in step with the other, so the challenge is to have a narrative where you can stop the sequence of things and have a thematic break from that and then return.
Leslie Mitchell has organised his book along thematic lines.
It houses a notable assemblage of British paintings displayed along thematic lines.
Indeed, in these works the moments of upheaval are muted; the thematic lines stand out in relief.
The Brahms was spacious, almost Wagnerian in places, with thematic lines singing out grandly and rhythms surging underneath.
He has tied together the museum's three thematic lines: archaeology, Jewish art and life, and the fine arts.
