I was recently called out for writing the following:

I understand perfectly, thank you.

Since ‘thank you’ can be taken to be an independent clause, this would seem to be a run-on sentence. It was my understanding, however, that ‘thank you’ functions as a tag in this case and that the sentence is therefore valid.

Am I correct?

  • 6
    Thank you functions as a tag there. Apart from that, it is really, really hard to create a run-on sentence of five words. – Robusto Mar 19 '15 at 9:56
  • I suppose the jury will remain out on that one forever. Grammar apart, the tagging gives an additional significance to the phrase in the overall meaning. – Kris Mar 19 '15 at 11:02
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    If your sentence, punctuated as it is, appeared in a novel by an author who was meticulous about his or her punctuation, and used it to indicate how characters delivered their words, I would understand it to mean that the speaker was a little cross or ticked off, as if he had been condescended to. – TRomano Mar 19 '15 at 11:52
  • Thank you can be considered a clause -- though it functions as a pragmatic interjection -- but it's certainly a tag and gets comma intonation before it, instead of full stop. – John Lawler Mar 19 '15 at 16:33
  • I agree with Tim Romano, that the speaker was ticked off. "I understand perfectly", when spoken, often means "why are you wasting my time by telling me this?" "Thank you. Now I understand perfectly." is completely different. – ab2 Jul 17 '15 at 19:37

I don't think that anyone would dispute that the sentence

I've had enough, thank you.

in reply to a host's asking if the guest would like some more chocolate-covered potato chips, does not constitute a run-on sentence. We're accustomed to hearing people attach "thank you" to a refusal of this sort as an appended signal of politeness, so we don't demand that the construction make sense as single entity when rendered in sentence-diagram form.


I understand perfectly, thank you.

has a lot in common with "I've had enough, thank you." So it seems to me that the crucial question from a reader's perspective is whether we are to read the "understand perfectly" sentence with the same continuous intonation as the "had enough" sentence, or if contrarily we are to read it as a truncated version of two separate sentence wrongly bound by a comma:

I understand perfectly, thank you [for your help/concern/interest].

In the latter case, of course, a stronger punctuation mark would convey the intended sense of the sentence successfully, where the comma does not. Either

I understand perfectly; thank you [for your help/concern/interest].


I understand perfectly. Thank you [for your help/concern/interest].

would do the job. But the writer knows which sense of the original wording was intended; and in the absence of a spoken version of the statement (where hearers could evaluate the statement's intonation for themselves), it seems to me reasonable to suppose that the writer intended the phrase to be understood in the same fashion as "I've had enough, thank you," and punctuated the sentence appropriately to convey that sense.

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  • The elephant in the room is that run-on sentences are not a problem in the first place. None at all. That is why they exist in the first place. You could write run-on sentences all day long, and in fact you spend your entire life speaking in run-on sentences. – RegDwigнt May 18 '15 at 10:15
  • I wish people (teachers) wouldn't call them "run-on" sentences, which gives students the impression that long sentences are undesirable. We talked about "run-together" sentences, which was the undesirable joining of two independent clauses with a comma. Which rule, of course, is open to plenty of exceptions. – ewormuth Aug 16 '15 at 15:36

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