Learners of a foreign language, especially at initial and intermediate stages, are basically taught its standard variety – provided there is such a thing. It is generally assumed that if you just use ‘common’ words and constructions, avoiding dialectal features, colloquial traits and slang of any sort, you will communicate successfully in most situations. After all, you are – and probably will always remain – a foreigner, and polite people can be expected to tolerate a good deal of contextual inadequacy. The problem is that, rather than being ‘common’, the variety taught is often rather that of grammar books; a system full of archaic constructions and old-fashiones rules that, in the case of English, can make you sound quite like a character in a Shakespeare play. And you probably don’t want polite people to start giggling (very discreetly, of course).
The problem stems to a great extent from the prescriptive tradition of grammar, which has often strived to assimilate modern languages as much as possible to Latin and Greek, attributing them many features of the Classic languages that were actually long lost. Here I will recall a handful of facts I was made to learn about English grammar which I later discovered were, well, not the whole truth.
There are cases. You cannot say The girl who I saw, since the girl is understood as the object of saw and thus who needs to be in its accusative form, that is, whom. It seems there are even vocatives in English, as Winston Churchill was well aware. But the truth is that our Barbarian languages do fine with prepositions, and sometimes even without them, just relying on syntactic ordering and some interpretive logic. Therefore, elegant and precise as whom may be, it has for long been going down the same path as Spanish (genitive) cuyo.
There is a subjunctive mood. When you express an unreal circumstance, as in a conditional sentence, you should use special subjunctive forms like were instead of was. Just remember the tune in that old movie – If I were a rich man, which you hardly are or have ever been. Well, no wonder English speakers should be envious of the conjugational richness of Romance languages, but the truth is that it’s quite OK to say If I was, and this is in fact what most speakers will usually say. It is also true that strange forms still surface in certain contexts, e.g. He suggested that she go home – is this go some kind of subjunctive-infinitive?
There needs to be number agreement in there is / there was. These constructions are not equivalent to Spanish ‘impersonal’ hay ‘there is’, which is immobilized in the singular – at least if you’re not a Catalan native speaker or a journalist. So in good, standard English you need to say There is a house vs. There are two houses. Then you will start talking to real people and note that at least the contracted form there’s is rather popular with plural phrases, to the point that a language connoisseur such as Madonna utters There’s no more places to hide in one of her songs. Some will go even farther and say There was two houses, but this one does sound kind of objectionable for your average King James Bible.
People and police are always plural. Well, that one seems to be basically true. It would seem to be a rule specifically designed for speakers of Spanish and other Romance languages, since the equivalent expressions are singular for us. See however the preceding point, whereby you’re authorized to say There’s many people – which obviously sounds much better than There are.
Double negation is ungrammatical. Again, the intent to prevent students from performing syntactic transfer from their languages – Spanish being a case in point – results in overstatement. Double negation is not ungrammatical in English, but just scarcely standard – there ain’t no denying it.
You cannot go out on the street without knowing all your phrasal verbs. This was the point that really made everyone freak out. I had to spent so many hours studying those devilish verbal compounds – I remember to bring up having at least six different meanings, of which for some reason I could only retain ‘to vomit’. The truth is that, first, most of them are not so frequent in discourse; second, many of them are not really phrasal verbs, but just verbs followed by a preposition whose meaning can be interpreted sequentially; third, if you still feel kind of desperate, you can always take a look at German verbs, with their hundreds of detachable vs. undetachable prefixes and the syntactic and semantic implications thereof, and you’ll finally rest assured that English is quite user-friendly.
And, well, now that I’ve gotten over the standard-only stage and I’m just a couple of (long) steps away from English nativehood – this non-existent term is at least a better solution than Nativity – I guess I ought to adopt the prescriptive stance I often exhibit in Spanish, thus complain that all those beautiful, classic grammatical rules should have fallen into disuse. Still, I seem to feel somewhat more tolerant about degradation when it affects languages I don’t make a living out of.