I'm reading a programming book and in it it is said, of a subset of engineers,

"Electrical engineers and systems designers who create computer motherboards and other hardware systems incorporating Intel processors need to know some of the rest, but they are a small and hardy crew, and they know who they are."

I unsuccessfully tried to find the meaning of that last bit on its own online. It seems to be an idiom. I would guess that it means that due to the small size of the group, the prominent people in it are known to one another and comprise a sort of community. Perhaps someone knows/has encountered the segment in question?

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    I suppose it's an idiom, but it's pretty literal. The people concerned are expected to know that the sentence refers to them, without having to specifically mention them by name. Commented Mar 11, 2021 at 18:11
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    They know who they are and they know what they did.
    – user121330
    Commented Mar 11, 2021 at 18:39
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    It isn't referrring to the fact that these people know who each other are, it's that they know who they themselves are. If you're an EE or system designer whose job is to create computer motherboards: Well, you know that that's who you are. Or, referring to the group of them (unknown to you) in the 3rd person plural: They know who they are.
    – davidbak
    Commented Mar 11, 2021 at 20:49
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    it means not you
    – Kevin
    Commented Mar 11, 2021 at 22:34
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    It's the author's way of saying that if you're one of the people who need to know the rest of the details, then you also already know what the rest of the details are, or at least you know where to find them. Conversely, if you aren't one of those people, then you don't need to know the rest of the details, which is why the author isn't going to include those details in his programming book. Commented Mar 12, 2021 at 2:08

3 Answers 3


The phrase "they/you know who they/you are" is typically used to address members of a subset of your audience without specifying their names.

We often use this phrase in an acknowledgement, or dedication, like you might find at the beginning or end of a book. An example would be:

This book is dedicated to all the people who supported me as I was writing it. They know who they are.

In other words, those people who supported me know that they are included in the group "all the people who supported me", so I'm not going to list each of their names.

Another common use - and one that perhaps makes more sense - is when you're admonishing a group of people in public, but want to spare them the embarrassment of being singled out. For example:

Some people have not yet completed the required training - they know who they are (because we sent them a reminder email) - and we're working with them to get the training finished as soon as possible.

Similarly, you might use this phrase when giving a public address because you want the general audience not to worry that you might be talking about them:

For those of you who forgot to sign up for a shift - and you know who you are - please email Alice by the end of the day.

In the quoted example, the author intends to say something like this:

The next section is not for everyone. It's only for people who need to know extra information about [whatever the next section is about]. The people who need to know this information are electrical engineers and systems designers who create computer motherboards and if you were a member of this group, you would know you were a member. So if you're not sure if this next section is for you, it's not.

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    Good explanation of possible variations in meaning, and a particular ovation for the final sentence. Commented Mar 11, 2021 at 0:57

It is an idiom. It stands for “I am not mentioning their names [to avoid embarrassment, argument etc] but those people know I am talking about them”. It is often said in a lighthearted way.

  • On the other hand: When John Lindsey was running for Mayor of New York City in 1965, he said he would challenge the "power brokers" who tried to run things in that city. When asked for names, he didn't give any, but said firmly: "They know who they are." At least one writer has asserted that Lindsey's subsequent bungling of his first few crises (after he was elected Mayor) indicated that the main reason he had been so vague was that he didn't know who they were, nor how important it was to learn to get along with them if you wanted to accomplish anything important.
    – Lorendiac
    Commented Mar 12, 2021 at 1:16
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    While this is a common use of the idiom, I don't think it applies to this case.
    – Barmar
    Commented Mar 12, 2021 at 14:42

It means that the people in the group know that they're in the group, not that they know each other, or that the speaker knows them. In the example, people doing that particular sort of hardware design know that they need to know the particular technical stuff the author's writing about, while other people really don't. But they generally aren't known to each other: if I design motherboards for a US-based company, I probably have no idea who my counterparts designing them for Chinese-based companies are.


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