Typically we talk about form in music in structural terms. A piece is in ABA form if it has an opening section, a contrasting section and the return of the opening section. Musical form takes place in time. But we also talk about musical texture. Some examples are "melody and accompaniment", "Alberti bass", "canon", "fugue" and "a capella". There are a whole lot of textures that we don't seem to have a name for like the pulsating repetitive structures we find in the music of Steve Reich or Philip Glass.
Theorists often refer to fugue as a texture rather than a form and yes, you can see their point. A fugue consists of a particular subject presented in different voices. Once this is done there is often a development section or "episode" followed by more presentations of the subject. These presentations can be varied by changing the order of the entry of the voices, by changing the time interval of entry (if a voice enters before the previous one is finished this is called a "stretto"), by inverting the subject and countersubject (invertible counterpoint), by inverting the subject, by augmenting or diminishing the subject (rhythmically) and so on. But these procedures are all available in whatever way or sequence the composer wishes. So "fugue" is not a structure or form that can be summarized in sections like ABA or ABACA or described harmonically as "sonata-allegro" form. It is instead many different potential structures.
I want to argue that there are lots of musical forms that don't submit easily to simple letter labeling and fugue is one of them. In other words, I want to argue that fugue, while an unusual family of forms or structures, is actually that and not a "texture". I want to say this because I think we can easily find good examples of musical texture that contrast well with the idea of form or structure.
Beardsley says that "It is possible to have a design with structure but not texture, or with texture but not structure." It is very easy to find examples in the visual arts as artists have pushed out to both extremes. How about in music? I think that while we don't find the extremes as often in music, there are enough examples to give us an idea of the difference between texture and structure. First of all, one extreme example might be John Cage's 4'33, which consists of three short movements adding up to that total duration. In each movement the performer is instructed to play nothing--each movement is nothing but rests. So what is this, structure or texture? I think this is a pure example of structure with no texture. The structure is the time durations but as there are no notes, there is no possibility of texture. A piece that leans pretty far the other way is any one of a number by Steve Reich. Let's pick the Octet as an example:
I think that most musicians would describe this as primarily a texture. Indeed, after about two minutes of this the flute enters with a melody which makes all the previous sound like an accompaniment. Steve Reich's music does have structure in the form of long-term processes, but you kind of have to gather them up in your mind to hear them. The surface of the music is pretty much exclusively texture.
One of the things that Beethoven did was filter out, more and more, the textural aspects of the Classical Style. What I mean by this is that the Classical Style had a lot of what you might call "filler" inherited from comic opera: things like repeated eighth notes in the cellos, Alberti bass accompaniments and a lot of other things designed to fill in necessary time intervals with activity. What Beethoven did was progressively to eliminate a lot of this and replace it with a small set of motifs--replace texture with something more structural. An excellent example of this is his Symphony No. 5 which eliminates a lot of conventional texture and replaces it with various manifestations of a simple motif and the associated rhythm. The effect is extraordinarily powerful:
On the other hand, here is an example in which structure of any kind has been eliminated and what remains is only texture:
I hope you listened to the whole thing? It's just so...
Bear in mind that there have been no aesthetic judgments as such in this post. I am just trying to discern two different elements in music: structure and texture. A simple minuet and trio could be an almost pure example of structure (especially if it is one of those canonic ones by Haydn) while a large piece by Steve Reich could be an almost pure example of texture. But a lot of the time avoiding structure while focusing on texture makes for a pretty poor composition.
The largest example of a piece that is almost pure structure that I know of is Bach's Art of Fugue which is largely based on a single theme and its permutations. Here is a great YouTube clip of the whole piece in the performance by the Emerson String Quartet, with the score: