The phrase "a main subject" is correct and usable in written English.
It can be used when referring to the primary topic or focus of a discussion, essay, or piece of writing.
Example: "In this research paper, the main subject is the impact of climate change on biodiversity."
Alternatives: "a primary topic" or "a central theme."
That is to be a main subject of negotiations in Thailand, probably starting next month.
Uncertainty in safety factor (FS) of slope stability is a main subject in geotechnical engineering.
La Sylphide (1836) stated a main subject of the Romantic ballet, the fight between the real world and the spiritual world.
North Korea was already expected to be a main subject for meetings on the sidelines of the Group of 20 economic summit, but the test adds urgency to a widening U.S. campaign aimed at further isolating North Korea.
This paper focuses on a main subject encountered in the design process of the hexagonal ducts etched in 〈1 0 0〉 silicon, namely, the achievement of the Poiseuille number Po for the velocity field of the fully developed laminar flow.
Force in biology has been a main subject in the field of biomechanics, which deals with the generation of force from biological activities and effects of applied force to biological structures.
As a place that has become a heartfelt staple to the idea of electronic music, the concentration of Detroit acts at the Movement Festival is always an main subject.
It's a measure of Anderson's skill that he can make a film whose main subject is loss seem so light-hearted and pleasurable.
In a way, their main subject is the wonder of the material itself.
In a parking lot, after a demonstration, Maddix's main subject protests that he isn't a racist.
I have made a career as a photographer and my main subject matter has been the normal; I try to show how extraordinary it really is.
