The other day I was cutting a mango using a sharp knife. I had sliced off one side of the mango and was then cutting a grid pattern in the flesh to be able to "open out" the side to eat the mango pieces. When cutting the grid I held my hand under the mango and had cut through the mango skin cutting my finger.

I exclaimed, "That will teach me to use a sharp knife when cutting up mango!"

My seven year old asked, "Don't you mean that'll teach you NOT to use a sharp knife?"

I then realized that it doesn't matter - at least to me - that I could have said it both ways and it would have meant the same thing.

So, my question is, do the two following phrases mean the same thing?

"That will teach me to use a sharp knife when cutting up mango!"


"That will teach me to NOT use a sharp knife when cutting up mango!"
  • +1 Ooooo! Ah luv it, luv it, luv it! An actual real live grammar question about real live actual grammar! :)
    – F.E.
    Feb 16, 2014 at 7:44
  • @F.E. - Yes, it was one of those moments when I had to stop and think. Feb 16, 2014 at 7:46
  • 1
    My father was a butcher, so when I was a child, I was taught at a young age how to use a knife safely. It was said that you were far more likely to cut yourself with a blunt knife than a sharp one. The first safety rule was , 'keep the knife sharp'. So, whilst I agree with your seven-year-old's grammar, I do not agree with the substance of the remark that you and he made.
    – WS2
    Feb 16, 2014 at 7:51
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    @WS2 Yes, I heard that it is safer to use a sharp knife than a dull one, as one tries too hard to make a dull knife cut through and that's what often causes one to pierce through one's skin, that extra sawing action.
    – F.E.
    Feb 16, 2014 at 8:00
  • @F.E. And always cut away from yourself, never towards you!
    – WS2
    Feb 16, 2014 at 8:10

2 Answers 2


The two written sentences can be interpreted differently:

"That will teach me to use a sharp knife when cutting up mango!"

can be interpreted as meaning:

This is the consequence (or, this is my punishment) for using a sharp knife.

The other sentence:

"That will teach me to NOT use a sharp knife when cutting up mango!"

could have a similar meaning, but it also carries more of an emphasis on future behaviour:

A similar example is:

That will teach me to be lazy! = I was lazy; now I suffering the consequences.

That will teach me not to be lazy! = I have learned my lesson not to be lazy in the future.

In spoken language the speaker wishing to convey the meanings I suggest is likely to place more emphasis on the beginning of the first sentence, and on the end of the second sentence:

That will teach me to be lazy!

That will teach me not to be lazy!

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    I'd say the negated version is a straight-up statement of fact, while the non-negated version has a strong element of sarcasm to it. Feb 16, 2014 at 10:15

The inherent difficulty in answering a question such as this is that only you know the precise meaning you were intending to convey with your initial statement. Without hearing the statement first hand we have no notion of any emphasis you may have placed in your utterance. If you stressed the word SHARP, it would suggest you were attributing the problem to be the sharpness of the knife (or rather, the lack of it). Without any stress on the adjective, the logical inference would be that you were commenting on your technique with knives in general regardless of how well-honed the given one might be.

So, if you intention was to state that the experience has taught you HOW to use a knife (sharp or otherwise) properly when cutting a mango, then both statements amount to the same thing as both suggest a better understanding of the technique for dissecting a fruit. By learning how NOT to do it, you also have a better understand of how to do it more effectively, and vice versa.

On the other hand, if you did stress the adjective 'sharp', then your intention could be taken to mean that a knife that is sharp (as opposed to the comparatively blunt one you did in fact use) would have been better. In other words:

That will teach me to use a SHARP knife when cutting up a mango—instead of a blunt one.

In this case the two statements, given by you and your child respectively, have opposite meanings. Your statement asserts a sharp knife is the way to go, the second, conversely, favours a blunt one. Here we might infer your child was thinking a blunt knife might be less likely to cut you. This is, of course, a logical fallacy possibly attributable to the child being only 7 years of age. As I suspect you are aware (and thus what I conclude you most likely intended by your statement): the sharper the knife the more precision it affords decreasing the pressure required and, in turn, the likelihood of subsequently cutting into an unwisely positioned digit beneath it.

A better statement altogether might have been to leave the knife out of the equation and address the real issue by saying:

That will teach me to hold the mango more safely when cutting it.

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