I'm just confused about why sonata form was innovative in the classical era, compared to the baroque era? was the structure used in the baroque era less organised??
closed as too broad by Carl Witthoft, Tim, Richard, Dom♦ Nov 4 '16 at 20:48
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Your question asks for a comparison between Baroque and Classical forms, and the answers to a question previously asked on this site provide a good summary of the different types of forms.
As you can see, many different forms existed in the Baroque period. Sonata form as seen in the Classical period was the culmination of years of evolution of structures that existed in the Baroque period. Sonata form has some things in common with previous forms; for example, binary form (AB) might feature modulation to the dominant before returning to the home key, as is seen in sonata form.
Things that made sonata form innovative include:
A 'standard layout' with rules about modulation and use of themes: exposition, development, recapitulation, (coda). Each section has a specific function in creating and resolving musical tension.
The use of short 'motifs' as thematic material, rather than single long themes (although this was a feature of the transition from Baroque to Classical in general).
The use of contrasting themes in different keys to create musical tension.
The reason sonata form has survived for so long is arguably because it features a satisfying mix of repetition and development that is absent in other forms.
Please note that whilst some of these features were typical of sonata form, there are many exceptions!
The Wikipedia article on sonata form is good as it provides a sense of how the different elements of sonata form combine to form a coherent 'musical argument'.