Omission of ne in the negative
Our overview of the French negative with ne ... pas described what people would generally consider to be the way negative sentences are formed in "standard" French (or at the very least, standard written French). For beginners, this is the recommended way to form the negative, and in particular in an exam, nobody will accuse you of "getting it wrong" if you stick to ne ... pas (and ne ... rien etc).
Unfortunately, there's just one problem with the ne ... pas pattern: it turns out not to be the way that native French speakers actually form the negative in many cases.
In informal speech (and certain types of writing that imitate informal speech), ne is commonly omitted from the negative.
Note that because omitting ne is a feature of informal French, it's often accompanied by other informal features. In these examples, notice the missing subject in y a pas de..., and the contraction of tu as... to t'as....
When is ne omitted?
When ne is omitted depends largely on the context, and to some extent on some other phonetic and syntactic factors.
The first thing to understand is that omission of ne is essentially a feature of informal spoken French.
That means that it is commonly found in relaxed situations among people who know each other relatively well (or occasionally in other situations such as an informal radio interview with a celebrity, where the people don't actually know each other, but speak as though they do). The word ne tends to be omitted much less in more formal situations when speakers are on their "best behaviour", such as when giving a speech or in a formal meeting or interview. For example, a politician giving a speech or interview would probably try and "monitor" their speech and avoid omitting ne, to avoid sounding overly informal— unless, of course, they are deliberately trying to create a surprisingly informal effect. (Note that this doesn't mean that "politicians never omit ne"— it just means that when wanting to give the impression of speaking formally or being on their "best linguistic behaviour", they would try not to.)
In writing, ne is usually not omitted, even in quite informal types of writing. The "written" contexts where it is omitted tend to be ones that are deliberately trying to imitate speech, such as:
There are a few phonetic (pronunciation-related) and syntactic ("grammar-related") factors that can influence whether a speaker omits ne. It's probably fair to say that these factors haven't been extremely well studied, but some factors cited by Ball, Colloquial French Grammar: A Practical Guide (2000:17-18) include:
The last point needs some explanation. A "phonetically marked" utterance is essentially one with an unusual combination of sounds (or a combination in an unusual position)2. For example, consider the following alternatives:
je n' veux pas de fromage
j' veux pas de fromage
Suggest a change / proposez une modification
Notice that we've deliberately written n' and j' even though they're followed by a consonant. That's an imitation of how speakers would generally pronounce these sentences: in spoken French, as informality increases, speakers generally tend to pronounce fewer of these schwa vowels (the vowel represented by a single e in writing).
The argument would then go that in this case, inserting the ne (albeit in its reduced form) provides a solution for still reducing one of the schwa vowels, and thus ending up with the rhythm of informal speech, whilst at the same time not starting the sentence with an unusual combination of sounds. In the second case, j'v... is a slightly unusual sound combination (although speakers do sometimes still use this variant of the sentence). What may influence the choice is how unusual that particular speaker subconciously feels this combination to be.
Another example where the speaker's subconscious preference may affect whether ne occurs is when il is followed by a verb beginning with a vowel (notably a and est). In such cases, the speaker effectively has a choice as to which "informal pronunciation" they use. If they omit3 the final l of il, as is common in informal French pronunciation, then without ne, they'd be left with (say) i' a pas. That would be interpreted as y a pas (e.g. y a pas de lait = il n'y a pas de lait). So to make sure that the listener understands il, the speaker has to opt for either the pronunciation i n'a pas, the ne allowing them to omit the final l of il, or else omit the ne but then have to include the final l of il: il a pas.
1. In other words, speakers would tend to say mon frère ne veut pas...
rather than ...veut pas..., because of the presence of the noun phrase mon frère.
Note that a problem with this observation is that a feature of
informal French is to insert a pronoun corresponding to the noun. For example:
mon frère, il (ne) veut pas venir vs the more formal
mon frère ne veut pas venir. So the statistic that we are looking at
could be the proportion of times that speakers chose a "more formal variant" of
the sentence rather than specifically a statement about how often ne is omitted
when an informal variant is chosen.