"the secondary theme" is correct and can be used in written English.
You can use it to refer to a theme that follows the primary or main theme of a story, film, song, or other cultural artifact. For example, in the movie Star Wars, the main theme is the struggle between good and evil, while the secondary theme is the power of friendship.
(If the principal subject is jealousy, the secondary theme is the power play within a Victorian marriage).
The primary material of the First Ballade rushes and relaxes in its searching progress, creating the conditions for the secondary theme, which is finely sung.
The secondary theme of this article is a triple integral for a 3-variable function q = q ( x, y, z ) in a domain D in the 3D space.
Betrayal is the secondary theme of The Wild Bunch.
In other related research, the secondary themes found in our study were identified as primary themes, possibly because participants in other studies sustained more severe injuries, and/or were predominantly over one year post injury [ 15, 17, 31].
The variety of colorings, shadings and nuances, as always, was wondrous: from the rich, mellow and dusky quality he brought to the wistful secondary theme in the fitful first movement, to the pale, spectral tone during passages of haunting arpeggio figurations in the slow movement.
The most important thematic connection is that the closing-phrase opening of the first movement reappears in the finale in a modified form: it no longer stands alone, but as the second part of an eight-measure phrase that forms the movement's secondary theme.
The proximity aspect of Tinder is subservient to the main component — dating, or more specifically a simple question of whether I fancy this face or not — and to the app's secondary theme — playing a game (of snap).
Existing research also relates these secondary themes to power imbalances and stigmatisation [ 15, 17], and perceived injustice; a multidimensional construct that includes unfairness, irreparability of loss and injury severity [ 21, 41].
The real value of "Worlds at War" may lie in a secondary theme: the West's long, tragicomic history of trying to civilize and modernize the East.
The Israeli-Arab conflict has been a strong secondary theme at the General Assembly, which has been dominated by the campaign against terrorism.
