I understand that you can't have a double negative...but also, 'anyone/anybody' in this sentence wouldn't make sense:
If I don't use the microphone, nobody will hear me
So why is this not considered a double negative? What is the logic here? Is it related to the IF clause?
In most forms of standard English, negatives don't agree with each other, each negative negates something separately.
So:
What people mean by not having double negatives is not that you can't have two negatives. It's that you can't have negative agreement. Negative agreement is where you say "I can't hear nobody" to mean that you can't hear anybody at all, or that you hear nobody at all. In negative agreement, the one negation applies to both words ("can" and "anybody"), commonly called a "double negative". Without negative agreement, "I can't hear nobody" would mean that you can hear at least somebody. Negative agreement is present in many languages, and variants of English, but generally not in variants of English considered "standard".
Usually you should reword sentences to avoid anything that sounds like negative agreement, so that it's not ambiguous whether you meant to use negative agreement or not. Your example, however, does not sound like something that could be negative agreement. This is, like you said, because they are two separate clauses joined by the "if" (and the elided "then").
The statement that one should not use a double negative is a caution against a particular dialect form well-known to native English speakers. It is something primary school teachers say to native speaking children. The caution should not be understood literally. It does not mean that all uses of double negation are incorrect.
A more precise statement of the rule would be: Standard English does not acknowledge negative concord. This dialect sentence displays negative concord:
If I don't use no microphone, no one will hear me.
Notice that in the first clause both the verb and its direct object are negated. This is negative concord because the two negatives are intended to reinforce one another.
As we have already said, standard English does not recognize negative concord. Instead double negatives cancel one another out to produce a positive. To illustrate this a teacher might ask the children to interpret the dialect sentence above as if it were standard English. The teacher guides them to an answer such as this:
I must not use a microphone if I want to be heard.
This is absurd of course. But it illustrates an important point: double negatives are not forbidden in standard English, they simple cancel one another out. It is only an error if negative concord was intended.
For example, this use of a double negative is good literary English:
Your complaints have not gone unheard.
The "not" and "un-" cancel one another out, so the sentence means:
Your complaints have been heard.
(Though the emphasis is a little different.)
The sentence in your question does not display negative concord like our dialect sentence. Nor do the negations cancel one another out (as in our example from literary English) since they are not in the same clause. Instead the two negations are in separate clauses joined in an if-then construct. We can simplify the sentence to this:
If no microphone, then no hearers.
We must use two negations in this sentence because the message is about two negations: negating the microphone negates the hearers.
A double negative is something of the form ¬(¬ P). The ¬ sign denotes negation.
Your statement is something of the form (¬ M) ⇒ (¬ H). The ⇒ sign denotes implication.
In classical logic, ¬(¬ P) is the same as simply P. In English, this is not quite so clear-cut, informal speech often uses double negative as emphasized negative instead.
But an implication statement is a different pair of shoes. (¬ M) ⇒ (¬ H) is actually logically equivalent to H ⇒ M, i.e.
If anybody hears me, I use a microphone.
Which would be a bit of a weird way of phrasing it, but it does express the intended statement. A more cromulent appropriate formulation would be
If anybody is to hear me, I must use a microphone.
$(\not M) \to (\not H)$ if ell.SE didn't (for some strange reason...) have MathJax disabled. In Unicode meanwhile, I found that → and ¬ both render so thin that I was worried they might be confused with one another. I guess ⟶ might work better. Then again, since about every discipline except formal logic uses double-stroke arrows for all implications, I daresay that's just fine here too.
Commented
Sep 19, 2020 at 17:55
Yes indeed. The if clause in the sentence makes a significant difference as compared to other common sentences.
If this would be considered in logical terms of computing world or mathematics, then it is very much possible to use double negation in a single sentence.
Also, as you already mentioned anybody/anyone simply doesn't make sense. No one/nobody is definitely the right term of usage.
The example sentence is probably not going to be considered as a "double negative" because the use of two negatives has not created more intensity. The two negatives "don't" and "nobody" appear to be used to assert an implication - "If no microphone, then no hearing", without intensity.
The logic for deciding whether a sentence includes double negatives is probably identification of a perception or intention that use of two negatives creates more intensity, as follows:
If "More intensity" = TRUE then "Double negative" = TRUE; if "More intensity" = FALSE then "Double negative" = FALSE.
For the example sentence it is probably indeed decisive that it is an "if-then" sentence. The separation of the two negatives across the "if-then" elements makes it unlikely that the two negatives create more intensity.
But in general, an "if-then" sentence construction might be inconclusive, when considering whether a sentence contains one or more double negatives. For example, variations on the example sentence that are still "if-then" sentences include:
"If I don't use no microphone, nobody will hear me".
"If I don't use no microphone, ain't nobody going to hear me".
These variations may be understood as saying the same thing as the example sentence — but with more and more intensity, where the two negatives "don't" and "no" intensify the "if" part of a sentence and the two negatives "ain't" and "nobody" intensity the "-then" part of a sentence. These variation sentences might be considered as examples of "double negative", on the logic identified above.
Double negatives would be "If I don't not use a microphone" or "nobody will not not hear me." A negative in one phrase (no microphone, not hear) doesn't apply to the other.
@FumbleFingers in a comment, answered:
The archetypal "double negative" for your cited context is “...nobody won't hear me.”
I understand that you can't have a double negative
Your statement is incorrect
It may be the source of your misunderstanding. In English you can have a double negative. The meaning however doesn't accord with the meaning in many other languages.
For example
"I don't not like ice-cream" in English means "I do like ice-cream". Would you ever use that expression? Yes, it's possible. Consider the following:
Mary: Let's get some ice-cream.
John: But you do not like ice-cream!
Mary: I don't not like ice-cream. It's not my favourite but I do like it in hot weather.
In that example, "don't not" is a double negative that means "do". The two negatives cancel each other because there is one verb.
In your original sentence there are two separate verbs. This is not a double-negative, it is two separate negatives.
This is more the case of hidden assumptions and overstating the impact for emphasis.
“If you don't use a mike,” the certain assumption is your voice won’t be as loud as it could be.
The hidden assumption is “Amplified” ;) that a mike,( amp and speaker) are needed for everyone to hear, yet some may hear it otherwise, but that’s insufficient.
This statement “treats the group as one“, so if some cannot hear, then the entire group cannot hear.
Thus the statement has loosely given unstated assumptions with a conclusion, rather than a simple statement.
“some may not be able to hear properly unless we use a “mike”
Neither example has a double negative adjective, just an assumed condition with an over-stated conclusion.
It is a logical if / then statement, not a self-contradictory statement.
For a statement to be a double negative, it must have two negatives with in the same statement. Since you have two statements in which one is dependent on the other, the negatives are not considered double. It's like saying 2-(-1) =, this equation is stating that a negative one is supposed to be taken away from two; so the equation (simplified) will be 2+1=. now if you have 2 - (-1) = __ - (-1) =, this equation would not be simplified to 2+2= because the next negative is only supposed to be read after the first part of the equation is finished. Now in English, if you take away the first clause, will the second clause make sense. So, your sentence with the second clause only would be "nobody will hear me." does this make sense by itself... if it does then it is its own clause and therefore a new statement, in this case a dependent clause. You wouldn't change the sentence to "one will hear me," if it was by itself. Now if you would have written, "nobody wouldn't hear me," then you will have a double negative because the meaning goes negative then positive with the second negative canceling out the negative and turning the meaning into a positive. Two negatives in the same clause.
