The order of terms matters even when they commute

From Why start at x, y, z

When writing an expression that consists of several terms, the conventions regarding their order appear arbitrary.


It is usual to write:

  • \(xy\) and \(yx\) in either order;
  • \(5t\) but not \(t5\) (to avoid confusion with \(t_5\) or \(t^5\));
  • \(x\sqrt{2}\) but not \(\sqrt{2}x\) (to avoid confusion with \(\sqrt{2x}\)). (See Something on the right of a radical)
  • \(\sqrt{2}\sin x\) but not \(\sin x \sqrt{2}\) (to avoid confusion with \(\sin \left(x\sqrt{2}\right)\)).


People sometimes rearrange a sum to avoid a leading unary minus, even when this contradicts the convention of writing terms in decreasing order of degree:

\[ 1 - x \]

instead of

\[ -x + 1 \]