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I'm curious about the correct usage of commas in the following sentence:

"Secondary electron emission from metallic and especially dielectric surfaces is a fundamental process of great technological significance."

I heard that one should put a comma before but not after especially. However, in my opinion the sentence looks kind of weird with a comma in front of especially. Can anyone assist me on this?

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  • The current set of answers are addressing the word "especially" when used to start a dependent clause. If especially is not being used in this manner, these are not the rules used. Example: "I am especially happy to see you". No dependent clause, no commas.
    – user99525
    Commented Nov 30, 2014 at 2:50

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The rule you were taught is an over-generalization. The sentence written above is correct with no commas at all. The "rule" about especially only applies to the case when especially is being used as a parenthetical phrase, usually at the end of a sentence.

We really like ice cream, especially chocolate ice cream.

This rule is not unique to the word especially, but is used for all sorts of sentence-final parentheticals:

The "rule" about especially only applies to the case when especially is being used as a parenthetical phrase, usually at the end of a sentence.

Since your sentence is not using especially to begin a parenthetical statement, it does not require a comma. It is, however, stylistically awkward, and I would recommend the following revision:

Secondary electron emission from metallic surfaces, especially dielectric surfaces, is a fundamental process of great technological significance

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  • Thanks for your detailed answer. However, as pointed out in my comment to Barrie England's answer your suggestion of commas does imply a logically incorrect meaning because metallic and dielectric surfaces are two different things. So I guess it's probably the best to not put any commas at all.
    – hennes
    Commented Aug 3, 2012 at 19:07
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    A dash between especially and metallic could help a reader in your case. "Secondary electron emission from metallic and especially-dielectric surfaces is a fundamental process of great technological significance."
    – techSultan
    Commented Oct 20, 2016 at 18:16
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If you put any commas in that sentence at all, then put one after metallic and another after dielectric.

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  • I agree the suggested form (which JSBձոգչ also mentions at end of his or her answer) is grammatical, but I think in this case it gives the sentence a different meaning because of implying dielectric surfaces are metallic, which they need not be.
    – James Waldby - jwpat7
    Commented Aug 3, 2012 at 18:59
  • @jwpat7 You're right. In fact metallic and dielectric surfaces are two perfectly distinct things. I want to mention both but put a stress on the dielectric ones.
    – hennes
    Commented Aug 3, 2012 at 19:02

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