Which musical note lasts half as long as a minim?

A crotchet - and the naming is one of the more confusing legacies in music. British names describe shapes: a minim is the small one, a crotchet has a hook, a quaver shakes. American names describe arithmetic: half note, quarter note, eighth note, which tell you immediately how they relate and require no vocabulary at all.

The British names are older and were once accurate. A minim really was the shortest note in medieval notation, before composers kept subdividing and left the name stranded - so the smallest note is now called the small one and is nowhere near the smallest. Below the quaver there are semiquavers, demisemiquavers, hemidemisemiquavers, and beyond that a naming system that has essentially given up.

Neither system says how long anything lasts. A crotchet is half a minim and no particular number of seconds - duration comes from the tempo marking, which for centuries was a word in Italian describing a mood rather than a speed. The metronome only arrived in the 1810s, and Beethoven's markings for his own symphonies are notoriously fast, which has produced two centuries of argument about whether his metronome was broken, he was deaf, or everyone since has simply been playing him too slowly.