|The coordinating conjunctions but and yet are often used to compare and contrast.
But can be used to indicate a contrast:
The Equal Pay Act of 1964 attempted to legislate equal pay for equal work for
women, but in 1973 it was still true that women were earning from 37.8 percent
to 63.6 percent of what men in the same job classifications were earning.
Yet is used to indicate an unexpected consequence:
Power technologies have eased and simplified thousands of jobs, yet the labor
market is still dominated by sex-typed occupations, despite the fact that the
worker's physical "strength" is no longer a relevant criterion.
The WriteSite's A-Z list of grammar topics has more information coordinating conjunctions. You can also check out the "Is It a Sentence?" section of Hot Spots.
— From "From Virginia Dare to Virginia Slims: Women and Technology
in American Life," by Ruth Schwartz Cowan