Beethoven's String Quartets, Part 1
I've seen this designation only in reference to his string quartets, but there are doubtless other places where it is used. The caveat, here, is that the dividing lines between these periods have works crossing over from one to the other. The periods have to do with Beethoven's growth and development, which seems to align with the musical styles of the various periods' works.
The difference between the Early and Middle compositional styles is quite stark and unmistakable.
The early quartets consist of one opus, Op. 18, but it contains six quartets. Only this, and his next set, the Razumovsky Quartets of Op. 59, contain multiple works published under one number. The remaining works, which are quite complex, are single works under a single opus number.
First, let me address the Early work, Op. 18, Nos. 1-6. The recording I have is of the Tokyo String Quartet. The quartets, on the surface, sound much like works of Mozart or Haydn, though I have seen references to how these quartets "stretch" the boundaries of Classical form. They are quite pleasant in much the same way as those of Classical composers, with emotional restraint and sticking to recognized forms.
The Op. 59 quartets were commissioned by a Count Razumovsky, who was the Russian ambassador to Austria and a patron of Beethoven. These three quartets sound like they come from a different composer in a different era. It is said that when the Count's standing quartet first played them, they thought Beethoven was playing a joke. These quartets completely abandon the Classical style, with an expression of emotion that sounds pre-Romantic. For example, the first movement of the first quartet have a sense of motion to them, motion that serves as a dialog amongst the strings. There was probably nothing that sounded like them anywhere up to that time, and must have been considered avante-garde, if not somewhat confusing.
The difference between these two sets of quartets is striking, though not shocking to modern ears two hundred years later. Between the two sets, I prefer the Op. 59, though I admit fondness for both.
There are two more quartets that are considered "middle" quartets, followed by a handful of "late" quartets, which I will cover next.