Rotate versus revolve

Q From Brian Miller, Australia: A loosely organised group of eccentric friends and wine lovers meets each week. The question arose, does a lazy Susan revolve or rotate? What about the plates on it?

A That’s an interesting question, which lacks a simple answer. If anybody’s not sure about a lazy Susan, by the way, it’s a device on a table which turns to give easy access to plates and condiments, though the term has been extended to similar devices fitted in cupboards.

Most people’s response to this would probably be on the lines of “who cares?” The two words are used so interchangeably in the sense of spinning round that for most purposes they’re synonyms and they’re treated as such in thesauruses. To take an example, does a wheel rotate or revolve? Most people would say it can do either.

If you’re arguing from etymology (always risky), it can only rotate, since that term is from the Latin verb rotare, to turn in a circle, whose root is rota, a wheel. But you might argue that it revolves, because that verb is from the Latin volvere, to roll (in this case, the re- prefix implies repetition of the action) and a wheeled vehicle certainly does roll along.

Strictly speaking, there is a difference, which is most noticeable in the terminology of astronomers. For them, the earth rotates every 24 hours but takes a year to revolve around the sun. The rule about which verb to use is based on the position of the axis of rotation. If the body turns on an axis within itself it rotates but if the axis is elsewhere it revolves. Following this definition, a wheel can only rotate (hooray for etymology).

The strict answer to the question, therefore, is that the lazy Susan rotates. However, because the plates on it orbit or circle around a point outside themselves, they revolve. Do not insist on this careful distinction during the later stages of a dinner party or the lazy Susan may become a spinning projectile aimed at you.

As I say, the rule is rarely observed outside science and the two words have been hopelessly muddled for centuries. A revolving door actually rotates, as does a revolving chair; a rotating shaft makes revolutions. You might argue that a revolver ought to be a rotator but it depends whether you are thinking of the cartridges or the cylinder that holds them.