This semester, to fill up three units I needed for the good student discount on my car insurance, I took a basic introduction to linguistics class. For my third paper in the class, I wrote about the evolution of the English declension system, from Proto-Indo-European to modern Standard American English (the type used in things like text books, which is a bit more formal and "high" than everyday English, but not all that much different). Unfortunately, as the paper wasn't supposed to be more than three pages, all I could really do was give a brief overview of how the forms changed (and even then you can tell I basically ran out of space in the last paragraph, and attempted to very quickly conclude the paper). Had it been a term paper (something more like ten pages), I could have also included such information as why the changes occurred, as well as some of my predictions for the future of English based on what I see today. In this post (and possibly future ones, depending on how lengthy this turns out to be), I'll talk a bit about the latter topic: the future of English and current trends (although here I'll address more than just declension).
First, and most relevant to the paper, is what is happening with declension today. As I mentioned in my previous comparison and contrasting of case between languages, I mentioned that English currently has two cases for nouns (the general and possessive cases), and three for pronouns (subjective - 'I' - objective - 'me' - and possessive - 'my' or 'mine', depending on whether the pronoun is acting as a noun or an adjective).
However, in modern day colloquial English (the type you'd talk to your friends with), the line between the subjective and objective cases of the pronoun are becoming blurry. It's now very frequent for native speakers to use objective pronouns even in the subject position (e.g. "Me and Josh went to the supermarket"). This is done even by people such as me, who know that that is technically incorrect (should be 'I', instead of 'me').
So, where is this development going? Unfortunately, while this is growing in prominence, and is thus likely to shape tomorrow's English, it's not entirely clear what that shape will be. There are at least three possible ways this could go. First, as some have suggested, the subjective case may be lost, and English will be down to two cases for pronouns, just like nouns. This is clearly something English could take in stride. We already use syntax (word order) to differentiate between nouns being the subject or object of the sentence (in a manner outlined in my paper), so the two cases are really redundant.
However, it must be noted that no native speaker of standard American English (I can't speak for other dialects, as I don't know about them) would say something like "Me went to the supermarket"; it clearly sounds wrong. There are two alternate hypotheses that take this into account.
First, the application of the subjective case could be restricted. Rather than being used for the subject of the sentence, the rule could be altered, so that the subjective case is only used for the subject of the sentence when the subject is only composed of one noun/pronoun (as in the previous example), ignoring whether it's singular or plural. While the names subjective/objective make this sound counter-intuitive, you have to remember that the objective case already functions like an oblique case (which might, perhaps, be a better name for it) - a catch-all that includes everything but the subjective. Given this, this possibility doesn't sound so strange; of course, the subjective case could still stand a better name.
Finally, there's a third possibility. This one is particularly attractive to me, simply because it would be so unusual; specifically, that we are seeing the creation of a new, additional case: the conjunctive case - one used when there are a list of two or more nouns/pronouns in a group (note that the possessive case behaves fundamentally differently than the subjective or objective case as it is*, and so wouldn't follow this new rule). In this case (pun not intended), the form of the conjunctive case is identical to the objective case. I suppose the surest proof of this hypothesis would be if the conjunctive and objective forms diverge in the future, while the subjective case is retained.
Lastly, a footnote about the possessive case. There are actually two forms of the possessive case: the noun form (e.g. 'mine') and the adjective form (e.g. 'my'). The adjective form is clearly distinct in use from the subjective and objective cases, as it is an adjective and they are nouns. The noun form of the possessive, however, is also clearly distinct. The reason for this is that it refers to something completely different than the subjective or objective case. 'I' and 'me' both refer to exactly the same thing - me; 'mine', however, refers to something completely different - something that is obviously not me. Thus its not unreasonable to consider the possessive forms as behaving fundamentally differently from the subjective or objective cases, and not require them to follow the same rules.