I have wondered if it is bad practice to learn only one movement of a sonata. I have heard some people say yes, and others say that it is perfectly fine. I am asking this because I once learned the first two movements to Mozart's K545 but I didn't learn the third. For future reference, should one always learn all the movements to a sonata?
Much to the ridicule of those who post here, I am a classical pianist/philosopher with nothing to back it up. However, as such, I always (as a scientific empiricist) cite a single or multiple sources directly related to my argument.
Regarding the OP, I cite an internationally recognized authority on original performance practice, which is the predicate to the thesis associated with my video. His name is Dr. Kenneth Hamilton, who is currently the Head of the College of Arts and Sciences at the University of Cardiff.
His New York Times reviewed book, "After the Golden Age," is considered the widely accepted source material on a basic level review of how the piano was originally performed in public in the 19th century. The point being:
So-called Classical Music (not the phrase used at the time) performances consisted of what today would be considered a "Variety Show." That means (as described by Dr. Hamilton), there was not one soloist.
A concert would start off with the orchestra playing and intro to an well known Opera, and then a piano soloist would come out and play a movement from either a piano concerto, or absent the orchestra, "A Movement From a Piano Sonata."
Next, a Chamber Music group would come out, and then so forth and so on.
Accordingly, until the late 19th century, it was a rare occurrence for a single pianist to perform an entire program. And, even if they did so, it no way resembled a "complete work" set of pieces as is performed today.
Hey, if you don't believe his book, Dr. Hamilton is most eager to discuss his work through email.
If so inclined, please contact me by PM.
All the best.