The phrase "a fair theory" is correct and usable in written English.
It can be used when discussing a theory that is reasonable, justifiable, or balanced in its approach or conclusions.
Example: "After reviewing the evidence, I believe that a fair theory can be developed to explain the observed phenomena."
Alternatives: "a reasonable theory" or "an equitable theory".
SCHOELLER -- The question is: Can we afford forever this free world trade theory, or shall we switch to what has already been discussed in Seattle -- a fair trade theory, where free trade can happen when a country applies certain minimum salaries and certain minimum ecological standards?
While these criticisms are fair, theories on disruptive innovation suggest that disruption in its early stages is often dismissed as a "toy".
There is a fair bit of theory but also some good demos and class practicals that they will be able to get their teeth into.
There is a fair agreement between theory and experiment but the agreement becomes poor with increasing segregation.
The idea was that the second "smaller bag" would fit under the seat in front of you, which is in theory, a fair idea.
IN THEORY Lebanon is an independent republic and in theory a democracy, which in theory rests upon a fair division of spoils between some 17 officially recognised religious "sects".
It's difficult to believe that you'll actually feel more refreshed with less sleep, but that's the theory; online, a fair number of people say that it works.
A circular bed had been exhibited in Vienna, i July, 1929; & other odd-shaped beds were in vogue in France & Italy during the late baroque period, but Mr. B. proceeded independently of all this, having evolved a theory that a fair number of people live in houses with round alcoves into which they want to put beds.
Wodehouse often shows a fair working knowledge of Marxist theory (the locus classicus here being the imperishable Mulliner short story "Archibald and the Masses"), and it isn't as far as you might think from Psmith, Journalist to Karl Marx, journalist extraordinaire.
