Theoretical, speculative, academic can be applied to minds, types of reasoning or philosophizing, or branches of learning as meaning concerned principally with abstractions and theories, sometimes at the expense of practical basis or application.
Theoretical in its most usual and nonderogatory sense applies to branches of learning (as sciences) which deal with the inferences drawn from observed facts and from the results of experiments and with the laws or theories that explain them.
In this sense the term is often opposed to applied , which describes branches of learning which have to do with the putting of such laws and theories into use (as in mechanics, in industry, or in social reform).
But theoretical often implies a divorce from actuality or reality that makes one unable to see things as they are and usually makes him see them only in the terms of preexistent ideas or theories. In this sense it is opposed to practical .
Speculative (see also THOUGHTFUL 1 ) may go further than theoretical in suggesting a deep interest in theorizing or in forming theories or hypotheses and often additionally implies a daring use of the imagination.
Often, however, there is very little difference evident in the use of these terms.
Academic (see also PEDANTIC ) carries a much stronger implication of a habit of looking at a thing, or things in general, abstractly, without reference to real life or practical concerns, and often in terms of the theories and dicta of a particular school (as of literature or art).