The phrase "a viable subject" is correct and usable in written English.
It can be used when discussing a topic or theme that is practical, feasible, or suitable for consideration or analysis.
Example: "The research team identified climate change as a viable subject for their next study due to its relevance and urgency."
Alternatives: "a suitable topic" or "a feasible theme".
There she found that the African fiction in which she had become expert was not a viable subject for a white Briton without any academic track record.
Much scholarship assumes it is the purview of journalistic criticism, and waits for consensus to arise before considering it a viable subject of analysis.
Anybody and everybody could be a viable subject for our films, as each of us has a particular set of life experiences which makes our perspective on the subject equally as valuable as anyone else's.
Therefore, a combination of our approach with RBM is a viable subject for future research.
Encouragingly, the advances we report here should help to make D. cylindrus a viable subject for research on coral early life history, and perhaps restoration, provided that gametes can be collected in sufficient numbers and that good fertilization rates are achieved.
But staying married like staying home is a far less compelling (though equally viable) subject for a story.
But staying married — like staying home — is a far less compelling (though equally viable) subject for a story.
The Dungeons and Dragons movie, released two years earlier––you know, the one you probably didn't see and had until now forgotten about entirely––certainly didn't offer much hope for dragons as any kind of viable subject matter.
Elsewhere he says scornfully that Walton and Britten are the best we can do in music, and that, indeed, we only excel in fiction "where gentility and the wretched English class system are actually viable subjects".
Fortunately, I've discovered ways to find inspiration and ideas when my brain isn't forthcoming with viable subjects on its own.
For starters, the left no longer has a privileged subject of revolution, as the figure of the worker and of the working class has disappeared as a unit of empirical reality and thus they no longer contain the same potency of agency and hence they are no longer viable subjects for producing social change (169).
