What does the double negation in this sentence actually mean?

Question

I was having a "comment chat" here on Workplace.SE when Alexander made the following comment:

But it's not just that most companies don't hire a permanent employee for a temp position.

Due to what seemed to be a double negation, I took it to mean "most companies hire a permanent employee for a temp position", which in context, was clearly not what he intended.

However, he then followed it up with a remark:

"not just ... not" is not "pure" double negation and its meaning cannot be resolved or simplifíed using boolean algebra.

Could someone explain to me how to interpret the original comment? Is there even any double negation at all, or does it use some idiom in a special sense that I am not aware of?

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Since comments could be deleted some time soon by the Workplace moderators, I am posting the relevant conversation here for context:

Masked Man: When evaluating such "ethical" questions in the workplace, I always find it useful to put the boot on the other foot: if the company has predecided to fire you after one year, would they tell you? That should lead you to the answer.

Alexander: But it's not just that most companies don't hire a permanent employee for a temp position. In fact, they do it the other way around: They hire temps for permanent jobs. So I am back to square one with the decision.

Masked Man: Was the double negation in your first sentence intentional? I took it to mean "most companies hire permanent employees for a temp position", which was probably not what you intended.

Alexander: "Not just ... not" is not a "pure" double negation and its meaning cannot be resolved or simplifíed using boolean algebra.

Answer 1

Mostly ditto Hellion's answer. Let me add one point:

People often say "two negatives make a positive" when discussing grammar. I've heard people try to simplistically count the number of negative words and declare that if there are an even number they cancel out and make a positive.

No. It is true that if you multiply two negative numbers together you get a positive number, but you cannot apply the rules of arithmetic to grammar.

In grammar, two negatives often make "zero". Like, "I am not saying no" is not at all the same as "I am saying yes". The two negatives don't make a positive, they make a vague neutral position.

Two negatives can make a stronger negative. If someone says, "I am not, I repeat NOT, going to do that", the second "not" most certainly does not reverse the first "not".

And often, as here, two negatives may be part of a more complex construction where different things are being negated. "I never saw someone get so disappointed to not get a birthday present." "Never" and "not" are both negatives, but they don't cancel out, because they are not talking about the same thing.

Answer 2

"It's not just that (X)" is another way to say "(X) is not the full extent of the problem."

In this construction, the target (X) can be almost any assertion, including a negative assertion. Generally, you will then follow it up with a more general version of (X) or an additional assertion (Y).

To take a shorter and hopefully easier-to-understand example:
"It's not just that he didn't call me" cannot be simplified to "it's just that he called me"; rather, it means that "the fact that (he didn't call me) is not the full problem." You would expect it to be followed by something like "he called my sister and asked her out instead."

In your sentences:

But it's not just that most companies don't hire a permanent employee for a temp position. In fact, they do it the other way around: They hire temps for permanent jobs.

The topic (X) is that "most companies don't hire a permanent employee for a temporary position". However, this fact is not the ONLY thing to consider; it's actually even more extreme in that not only do they not hire Perms for a Temp job, they don't even hire Perms for a Perm job.

Also, as @jay points out, this construct is not limited to expressing a problem; you could equally well use it to explain why you like someone: "It's not just that they're physically attractive, they're also kind, gentle and thoughtful."

Answer 3

It's not just that you were making noise late last night: you were making noise that kept me awake the night before the oral defense of my thesis!

How to understand "It is not just" + that-clause....

Here, just is a synonym for merely.

The fact that you were making noise is not, in and of itself, the only issue. You were making noise on an especially inopportune night.

That you were making noise is not the only concern...

I am upset not merely because you were making noise. No, you were making noise on a night when I really needed to sleep in order to be fresh the next day.

Answer 4

At the risk of merely reiterating the other answers — Alexander mentioned Boolean algebra, and that can be useful here, once we realize (as Jay said) that it’s not simply a matter of counting negative terms and discarding them pairwise.

A simple statement (X) means

The truth = (X)

But “just (X),” “merely (X),” or “only (X)” (with wording adjusted for grammar) means

The truth ≯ (X)
(is not greater than)

Yes, it also means that the truth = (X), but it emphasizes the aspect that the truth is not more than (X).

The phrase “at least” is subtly implied in many sentences; for example:

• You must be three feet tall to ride the roller coaster.
• You must be 18 years old to vote.
• This job requires that you have two years of experience.
• You should drink eight glasses of water every day.
• I ate three apples yesterday.

and so, if I say, “I ate only three apples yesterday,” that means that I ate three apples yesterday and no more.  So, if “just (X)” means

The truth ≯ (X)

then it follows that “[It’s] not just (X)” means

The truth is not ≯ (X)

Algebraically, this reduces to

The truth > (X)

i.e., not only is (X) true, but more.

Answer 5

The phrase "not just" does not mean "not". It means:

this "thing" is one member of a set

For example: But the days of the week is not just Thursday.

The above sentence does not mean that Thursday is not a day of the week. Instead it means almost the opposite: Thursday IS and element of the set we call days of the week.

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Therefore, to parse the sentence:

But it's not just that most companies don't hire a permanent employee for a temp position.

We can say that:

Concerning the implied subject of "Problems With Company Hiring Practices"
(perhaps referred to earlier in the conversation) {
  Companies not hiring permanent employees for temp positions {
      Belongs to the set of "Problems With Company Hiring Practices"
  }
}