I was baffled to find this in the introduction to a textbook:
We hope that readers will find this text offering them a useful introduction to and a basic treatment of [...], as well as preparing them for more advanced studies of this exciting and comprehensive subject...
Aren't all subjects comprehensive by definition? Comprehensive with respect to what?
In my opinion, not much thought has been put in to this sentence however it can have some meaning. I believe the meaning the author wants to achieve in this text is something along the lines of "as well as preparing them for more advanced studies of this exciting and extensive subject...".
A subject can't really be comprehensive as comprehensive is sort of like how in-depth something is. For example, to do something comprehensively is to do it thoroughly - covering all aspects in sufficient depth to be comprehensive. The boundary between whether something is comprehensive or not is a grey area and should be judged by someone with authority.
Comprehensive basically means all-inclusive, covering all related information. I think the phrase "comprehensive subject" is an example of poorly chosen word blending. One could deal with a subject in a comprehensive manner by saying all there is to say about it, for example. But by definition a subject would be considered comprehensive in that the subject contains all material related to the subject as part OF the subject. You could not say someone is a "comprehensive person". The term is not being used correctly. Same thing here.
The phrase "Comprehensive subject," is one that I've heard plenty of times, but a quick search on Google doesn't come up with many examples. My understanding is that the adjective comprehensive when related to the target noun subject is describing a:
As containing/including an adequate amount of information to answer questions without having to extend outside that particular subject or field.
Of course you make the point of asking, "with respect to what?" which I think depends on the context in which it's used. Something that is considered comprehensive in one context, may not be comprehensive in another.
A Biology professor may choose a certain textbook over others because it is comprehensive with respect to the course materials, the goals of the course, and/or the topics within biology that are meant to be covered in that particular course.
Your quote from the text includes "Treatment of..." but doesn't say what that treatment is... which may be what the subject is referring to.
Does the text go on to say"the comprehensive subject of art/painting/sculptures/or any thing like it." In that case ,even if we know the subjects are, by default, all encompassing,we cannot resist the temptation of mentioning for the sake of mentioning only because it adds a flair to the style of writing and comes automatically.
It could have been better if a few words after " comprehensive subject" are provided.
