Imagine one has to give a presentation to explain something to an audience which already knows very much about that topic.

Is that correct to say in such a situation that one is teaching fish to swim? Can I share the idiom with the audience?

E.g., "I'm afraid I'm teaching fish how to swim, but.."

And, are there any other expressions like this?

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    ...do fish swim? – RyeɃreḁd Apr 15 '14 at 5:32
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    The old expression for this was "teaching your grandmother to suck eggs", but your metaphor is more easily understood (and original, as far as I know). – Malvolio Apr 15 '14 at 5:56
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    Mari, to give someone a break is to treat someone more graciously, to make allowances for. Your question is completely understandable. I think it is kind of you to want to acknowledge the level of expertise of your audience. – anongoodnurse Apr 15 '14 at 6:14
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    In Poland, is teaching your father how to make babies ;) – Danubian Sailor Apr 15 '14 at 10:26
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    Another idiom very similar would be "preaching to the choir". – Mike H. Apr 15 '14 at 16:39

Teaching grandma to suck eggs, or teaching your grandmother to suck eggs is the unequivocal idiom which means giving advice to someone who is already an expert in the subject or field. There's also the implication that the "teacher" in question is less-experienced than their pupil.

Teaching fish to swim, although easily understood and to my ears, more contemporary, (who sucks raw eggs nowadays?) I don't think it has entered the vernacular, not yet anyway. According to Wikipedia

Teach fish how to swim is an idiomatic expression derived from the Latin proverb piscem natare docem. The phrase focuses attention on the self-sufficient perception of those who know how to do every thing better than the experts. [...] A corollary idiomatic phrase is part of common usage in Chinese (班门弄斧)

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    As a native English speaker, I don't think I've ever heard the phrase "teaching grandma to suck eggs," and if I did I'd be much more confused than if I heard "teaching fish to swim." – Kyle Strand Apr 15 '14 at 15:12
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    @KyleStrand Indeed, also as a native English speaker, if I encountered this expression I might think the speaker was being insulting, derogatory, or at the very least somewhat uncouth. – Michael Apr 15 '14 at 15:52
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    What the hell does it mean to "suck eggs"? To eat them like a soup? like a popsicle? to retrieve them from the hen? Oh, to take out the insides without damaging the shell. I will have to teach my grandmother about this, and she will think I am strange. – dezman Apr 15 '14 at 16:46
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    @watson My Italian mother used to live on a farm in the 30s and she would pierce both ends of the egg, still warm from the hen's nest, with a needle and suck the contents out. Times were hard, food was scarce and she was one of ten children! – Mari-Lou A Apr 15 '14 at 16:51
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    @Mari-LouA - This is why I like ELU. This is not a good phrase to say in the US. First it isn't used. And its close phrasal cousin - suck an egg means to fuck off. urbandictionary.com/define.php?term=go%20suck%20an%20egg So basically I would take this as teaching your grandma to fuck off - seriously. – RyeɃreḁd Apr 15 '14 at 17:19

Apparently my stack exchange reputation doesn't carry over between sites, so I can't comment on previous answers. I just wanted to add that "preaching to the choir" is more about not needing to convince someone of something, because the proverbial choir is already on "team jesus".

Also, "teaching [one's grandmother] to suck eggs" strikes me as very region-dependent. If someone said this to me, having grown up in southern california, I'd have no idea what they meant. I mean, I would now, because I read the other answers. But I wouldn't have 10 minutes ago. Could be misconstrued as something vulgar, or maybe a very awkward non-sequitur.

"Teaching fish to swim" is probably closer to what OP wants. It might not be part of everyone's common parlance, but it's at once clear what the speaker means, and doesn't feel at all awkward.

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    Once you get some amount of rep on one site (I can't remember how much), you get a +100 bonus on all sites. However, rep is never shared between sites (for the obvious reason that being an expert in one subject doesn't necessarily make you an expert in another). – Kyle Strand Apr 15 '14 at 15:15
  • @Kyle at 200 rep you get +100 association bonus. – MikeTheLiar Apr 15 '14 at 17:41

Yes, teaching 'fish how to swim' is indicating you understand their proficiency on the topic.

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Similar expressions included "Carrying coals to Newcastle" (where a lot of coal is produced), or "Taking owls to Athens" (Athena was the goddess wisdom).

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Yes it is proper to use teaching fish how to swim in your situation.

I know that explaining (topic) to you guys is like teaching fish how to swim...

Another phrase that comes to mind:

I know that I'm preaching to the choir, but today I would like to discuss (topic)...

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    Preaching to the choir has more of a 'share my beliefs/opinions' meaning rather than what's implied in the OP. – Joe Apr 15 '14 at 12:14

From wikipedia:


Teach fish how to swim is an idiomatic expression derived from the Latin proverb piscem natare docem. The phrase focuses attention on the self-sufficient perception of those who know how to do every thing better than the experts. Those who would attempt to do so are thought to exhibit a combination of hubris and arrogance in trying to engage in a needless exercise for which they are ill-equipped...

I would have to concur with Frank... Just saying, 'this may be an area most of you are familiar with' would suffice.

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  • This would be true if the OP pretended to know more about the topic than her audience, instead she realizes full well that the opposite may be true. By sharing the joke, "I'm afraid I'm teaching fish to swim, but..." the OP is actually preempting any negative feedback that might be aimed at her presentation. I think she is approaching the talk in the right spirit. – Mari-Lou A Apr 15 '14 at 22:05
  • I agree that there is more to communication than just the words used and hubris or arrogance could me mitigated with the right tone and body language. However, there is also a possibility that some folks may perceive the speaker as being intimidated by his audience as well.. My personal preference would be to eliminate any probability of being perceived as arrogant or intimidated...however slim the probability. – Keneni Apr 15 '14 at 22:23

I think 'teach fish to swim' has very negative connotations about yourself.

I really only know the phrase from 'He would try to teach fish to swim' meaning someone who believes they are so knowledgeable they can improve on anyone's learning, even to the point of improving an innate behaviour, implying a high degree of arrogance.

I see a similarity between 'teaching fish to swim' and 'teaching grandma to suck eggs' but the fact that for fish, swimming is innate and for grandmas, egg sucking is learned makes quite a difference.

If you are concerned about using the phrase, I wouldn't use it. To me it sounds like you could just as easily say 'I'm wasting my time, and yours, going over something you all know better than me'. It's a very negative start.

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    I think if it were used as the OP suggests, it would be more humorous (a self-deprecating humor perhaps, but still). If you do have to give a presentation on something people already know a lot about, why not bring it out in the open? – Joe Apr 15 '14 at 12:17
  • It seems like people familiar with the idiom might find it a little confusing, but if you don't know what it means then the use is extremely clear and self-explanatory. – Bill K Apr 16 '14 at 1:36

"Preaching to the choir" is quite popular.

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    "Preaching to the choir" refers to trying to persuade someone who already agrees with your opinion. I don't think it applies that well to the situation OP describes. – p.s.w.g Apr 15 '14 at 17:54
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    I think this is quite possibly closest despite not quite being spot on. – Vality Apr 15 '14 at 22:36

Another saying that comes to my mind is:

you know the long and short of it

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