Symphonies and sinfonias are they the same?

Question

Bach and many other composers composed many sinfonias as italian overture, operas and also for separate work. Symphonies, having a similar name and all, does it have anything to do with the sinfonia? are they similar or are they the same?

Answer 1

Broadly the symphony as we now know it grew out of the 'sinfonias' used as an introduction to Italian opera in the early 18th century. As the form grew and became in dependant during that century the term 'sinfonia' and 'symphony' were to some extent interchangeable, although the sinfonia in its original form usually had three movements (fast-slow-fast), but then so did many works called 'symphony'. By the time of Beethoven sinfonia had fallen out of use, although it was later used by composers who wanted to identify a work as lighter than a mainstream symphony.However, Britten entitled a work 'Sinfonia da Requiem' which is anything but light, but perhaps because he cast it in three movements

Later: I thank del_icio for his kind remarks, and would only add that I answered the question on tha basis that the question was aimed at the English  language (and to be fair, other languages) differences between, and usage of,  the two words. Of course, the Italians do not differentiate for as del_icio rightly states sinfonia is Italian for symphony and the question could not arise in that tongue

Answer 2

As rdenig_m states, the Classical era symphony evolved out of the Baroque era opera overture (which was also referred to as  a "sinfonia").  From the mid 1700s onward, sinfonia and symphony were essentially synonymous terms for the same type of composition.  Somewhere along the line the term sinfonia died out, with "Overture" being used for the instrumental introduction to an opera, and "Symphony" used for a free-standing orchestral piece in 3 or 4 movements.

During the late Renaissance and early Baroque periods, the term "Sinfonia" was also sometimes used for single-movement instrumental pieces in polyphonic form.  For example, Bach used this name for his Three-part Inventions for solo harpsichord.  

Answer 3

while rdenig has given an excellent explanation of the 18th century 'sinfonia' one has to remember that 'sinfonia' is also simply the Italian for 'symphony' and one can see this word being used for large-scale works (especially in Italy!).