The possessive adjective in English must be the most difficult grammar to master.
When is it a plain old adjective such as a car door? Or is that really a compound noun? When is it possessive as in a hair’s breadth? Is it a woman’s leg, or a woman leg? Or is at a chair’s leg, or a chair leg? There are many examples of this confusing English grammar point.
You would say the tree’s leaves, a butcher’s hook, a horse’s tail. Or you could say a bottle top, a door handle, a computer screen, day break, mountain top.
There is an obtuse grammatical explanation about ownership and being part of an object, but I won’t go there as the exception list is so long. I think in this case the exceptions really are the rule. The point about possessive adjectives is that they are impossible to learn by any process other than natural acquisition by repetitive collocation. By this, I mean that by hearing and using a phase correctly enough times, it becomes automatic, and thus the error is corrected. For learners of English, this can be very frustrating.
I have often heard it said that English is a relatively easy language to learn. In many ways, I agree with this. However, I would have to say that it is as difficult as any language to master. While having no grammatical gender or accordance of singular and plural adjectives, it does, however, have a grammatical and lexical complexity stemming from its multiple roots in German, French, Latin and Old English but to name a few. An example of this is the word blonde, or blond. I stand to be corrected, but I believe this to be the only English adjective that changes with the gender of the noun. A relic of French grammar.
The challenges of English grammar are a daily dilemma for experienced writers of English. Spelling, punctuation, vocabulary, collocation and tense all offer a wonderfully diverse set of rules, uses, exception, variants and accepted new forms. When did you last see the word whom, and who remembers how to use it correctly? When did it become accepted to finish a sentence with a preposition? I am pleased though that splitting the infinitive is still not acceptable.
English has the largest vocabulary of any living language and grows at a rate of approximately five thousand words every year. It is now well over one million words. It is one of the richest, most commonly used and evolving languages in the world. This, however, makes the task of using it correctly a challenge for all of us who work with our incredible language.