The definition for “Invention” in the Oxford Dictionary of music is the following is the following:

Name given by J.S.Bach to 15 of his shorter keyboard comps. in 2 parts or ´voices´,inc. in his Klavierbüchlein*, 1720. They are highly contrapuntal, being largely imitative in form. Each works out some short melodic motif. Bach also left another 15 comps. in the same style, now known as his ´3-part Inventions´, to which he gave the title ” Symphonies”.

Michael Kennedy, Joyce Kennedy and Tim Rutherford-Johnson, 2013

The description above indicates, that an invention is basically a shorter, smaller form of a fugue and sometimes even a canon, which has one motif that is being presented in varied forms throughout the piece. The simplicity of those 30 pieces was created on purpose; Bach’s intention was to write those pieces for younger pupils to study.  (1)

*Klavierbüchlein (Ger) = “Small piano-book

  1. Heukäufer, N.(2014). Musik Abi –  Kompaktwissen Oberstufe. Berlin: Cornelsen Scriptor, p. 112