  Colloidal particles are distinguishable. Moreover, their thermodynamic
properties are extensive. Statistical Mechanics predicts such behaviour if one
accepts that the configurational integral of a system of N colloids must be
divided by N!. In many textbooks it is argued that the factor N! corrects for
the fact that identical particles (in the quantum mechanical sense) are
indistinguishable. Clearly, this argument does not apply to colloids. This
articles explains why, nevertheless, all is well. The point has been made
before, but has not yet sunk in. I also discuss the effect of polydispersity.
