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When is it appropriate to use a hyphen?

I am unsure if and when to hyphenate steady state (in a mathematical context), i.e.:

We now calculate the steady-state concentration from the given formula.

I looked at this generic hyphenation question, but the links given there did not give a clear rule for this case.

To me, it seems most natural to write:

This is the steady state described by the formula.

But, at the same time:

This is the steady-state concentration described by the formula.

That is, hyphenate if it describes another noun but not if it stands on its own. Does that make sense? Searching for books on Amazon brings up titles with both steady state and steady-state which seem to at least partially conform to this rule.

Or would it be better to just chose either hyphenation or no hyphenation and then stick to that consistently?


Steady is an adjective which modifies state in all these cases. So where state is the noun, there should be no hyphen. Where steady and state are used as a single adjective - a compound modifier - for another noun (concentration, in your first example) they should be hyphenated.

In other words, your instinct is correct.

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