The Symphony History

The symphony has its origins in the baroque period, but the development occurs mainly throughout the eighteenth century. The eighteenth century is known as the Age of Enlightenment, and is a time when the middle class becomes important, and learning is focused on that is natural, able to be observed, and makes sense. Music is thought of a luxury, but a luxury that anyone could enjoy. It was not to be too complex, or emotional, or adventurous. It should be simple, pleasing to the ear, and have regular cadences and phrases. Symmetry, balance, logic, etc.
In Baroque, the musical interest is split between the two outermost voices, in Classical, it is singly in the highest voice, with everything else serving as supporting harmony.
Harmonic rhythm is slower, also. The harmonic rhythm is the speed that the chords change. In Baroque music, the chords and bass line move very quickly, "walking" from one harmony to another. In the Pre-Classic and Classical Periods, the rate of chord changes slows down, as the melody maintains the interest now.

Cosmopolitan style of European Music, rather than French traits, German contributions, etc. Italian poets were in Germany, German composer's in France, etc.

The underlying philosophy of the four-movement symphonic form is to progress from more to less difficulty.
The first movement has the most challenging material, themes, development, form, etc.
The second slow movement is longer, but easier to listen to, with a very basic form.
The third movement is a short dance movement, which is easy to enjoy.

The finale, or fourth movement, is usually very fast, but has little modulation or challenges for the listener. It is easy to follow and enjoy, and will be over soon!