There is an idiomatic expression in my native language: "You are confusing sour with yellow", which means something like that though lemons are sour and yellow, not every yellow thing is sour, and not every sour thing is yellow, and discussing their taste should not be substituted (intentionally or not) by discussing their color. In Russian, it would be "Вы путаете кислое с жёлтым".

Is there an equivalent in English?

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    You can't judge a book by its cover. Does this idiom suffice or is your native expression more nuanced in some way?
    – user405662
    Commented Jun 2 at 16:35
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    What a beautiful expression. More poetic than confusing correlation with causation. Commented Jun 2 at 16:39
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    @user405662 We have exactly the same expression, but I would say the meaning of "book" and "yellow" examples is completely different. "Don't judge a book..." is OK if we are talking, for example, about a strict but thoughtful and not cruel parent. I don't remember a real-life example for "Sour vs. Yellow" example for now, but it is used completely differently.
    – jsx97
    Commented Jun 2 at 16:43
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    Just curious, what is your native language, and what exactly is the expression? Commented Jun 2 at 16:50
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    If it looks like a lemon, smells like a lemon, and tastes like a lemon, then it's probably a lemon; whereas if it's just yellow, it could be a duck. True, but I'd probably use conflating instead. Commented Jun 3 at 4:59

4 Answers 4


I don’t know of an English equivalent to “you’re confusing sour with yellow.”. I wish we had one.

What we have is category error (https://en.m.wikipedia.org/wiki/Category_mistake), which is more formal and not an expression likely to be heard outside of academic circles, or perhaps programming. Examples of category errors often focus on the failure to distinguish the whole from its parts.

We also have, of course, Venn diagrams, as part of set theory.

But English has no saying that makes the point through an example.

  • Don't you think association fallacy works better than this? I don't see how exactly the "lemon example" is a category mistake.
    – user405662
    Commented Jun 4 at 2:27
  • I don’t think so. Rather, it’s like putting things in order by (say) weight, and then saying “Where does orange go?” Or “where does square go? Does it go between one pound and two pounds?”
    – Xanne
    Commented Jun 4 at 2:56

There might not be an precise English equivalent of the poster's native expression (as has been said above) but I think this idiom should do the job.

the proof is in the pudding

The proof is in the pudding is an expression that means the value, quality, or truth of something must be judged based on direct experience with it—or on its results. The expression is an alteration of an older saying that makes the meaning a bit clearer: the proof of the pudding is in the eating. In other words, things must be judged by trying them yourself or seeing them in action, rather than on other factors, such as hearsay.


Not an exact fit with the OP's “You're confusing sour with yellow” but ‘close enough’

You're barking up the wrong tree

Said when a person has mistaken something similar for something different entirely. It can also be used for when the solution to a problem is not working.

Scientists in Switzerland realised that most other researchers had been barking up the wrong tree.


The standard idiomatic Anglophone usage here is...

You're comparing apples and oranges

enter image description here

...where I've included the wildcard to show that whereas the first element is almost always apples, sometimes the second one is pears, bananas, potatoes,... But they're all used in the same way (pointing out that you're treating two things as "the same" when they're not).

It's worth noting the rather unusual appearance of You're comparing apples with apples. I'm not familiar with that usage, but I assume it's just a whimsical way of saying Don't confuse these [metaphorical] apples with those apples, because in the current context they're not comparable.

Plus of course there's Shakespeare's All that glisters is not gold (that's a link to an ELU question about the usage). That better matches OP's "Not every X thing is a Y thing", which isn't quite the same as "You can't compare X and Y". But both expressions are often used in similar contexts ("You're erroneously conflating two different things").

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    I don’t see apples and oranges as having the same meaning. OP’s aphorism warns against errors in syllogisms, or something close. Commented Jun 2 at 16:46
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    Don't get too hung up on the literal meaning. The contexts where we say apples aren't oranges are often exactly the same as the contexts where we say some glittery things aren't gold. The underlying meaning of the former is effectively Just because they're fruits (like apples) doesn't mean oranges are apples, which is much the same as Just because it glitters (like gold) doesn't mean it is gold. Commented Jun 2 at 16:51
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    Yes. (Without reference to the 'metaphor' reference above.) A metaphor brings out a valid point of comparison between two very dissimilar things. This is essentially about wrongly insisting that two similar things are totally alike. The false equivalence fallacy. Commented Jun 2 at 19:06
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    @FumbleFingers I didn’t get too hung up on the literal meaning, and I still think the suggestion of “compare apples and oranges” is the exact sort of tortured-meaning garbage that makes me embarrassed to visit ELU. It’s as if you purposefully misunderstood what the question asks. The real comparison of apples to oranges is comparing the idiom the asker posted with your suggestion, because they have nothing to do with each other. Commented Jun 3 at 6:53
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    You're confusing metaphors about fruit with yellow.
    – dleavitt
    Commented Jun 4 at 5:37

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