Grammar is the bony structure of language. It is the frame or skeleton that holds words together so that they can take on a meaningful shape to communicate a thought or feeling. Without grammar, or more properly without what is called syntax, grammatical arrangement, we would be left with randomly throwing at the reader one word after another in whatever order or shape those words might happen to assume as they occur to us. To the reasoning mind, that way madness lies.
But what does it mean to say that words have a shape? We know, certainly, that the three words I, my, me, for example, all have to do with the same person, though each has a different shape, or form, by virtue of being spelled differently. So, too, with the words we, our, us and who, whose, whom: each points to the same entity, called the antecedent, but some difference is intended with each distinction. This meaningful change in shape is called inflection. Some languages, like Latin, are greatly inflected (an adjective in Latin has potentially 36 different forms); other languages, like English, are negligibly inflected. And thankfully so.
Negligibly, perhaps, but not randomly. And so we have to come to terms with this much-too-commonly-heard lapse of you and I where syntax and inflection require you and me. When a question of grammar arises, it is best to begin the investigation with syntax: identify a meaningful section of the sentence and put that section under the grammatical microscope for analysis. In the sentence I want to tell you something, but it’s just between you and I, the specimen under the scope would be between you and I, because between is a preposition and every preposition requires an object. These together create a prepositional phrase, and a phrase is always a good sample to analyze.
The preposition between in the phrase we are examining has two objects, you and I, and we remember, next, that prepositions require their objects to be in a certain form, or inflection, in order to hold the phrase together and transmit meaning without unnecessary static. The two personal pronouns, you and I, each have three forms (you, your, you and I, my, me). These three forms, called cases, each have a specific function: the first, called the nominative case, is used when the word is a subject (you go, I stay); the second, called the possessive case, is used to show possession (your dog, my cat); and the third, called the objective case, is used as the object of a verb or preposition—always, no matter how resolutely your ear may squirm and squeal. Thus we conclude between you and me, not I, is correct. If grammar is the skeleton of language, then its parts must fit to function well. Once we know that things are in order, we can change them ever so cautiously and then only to a certain extent for effect, but that license belongs to the kingdom of style (to whom the ear is beholden), and even there, only tyrants do not obey the laws.
Checking our work in revision, then, includes the grammatical analysis of doubtful sections of sentences. We first ascertain exactly where the problem might lie (it’s this tooth, doctor, right here), and then look more exactly at the arrangement and form of the words that make up the troubling section. This close work helps us achieve clearness, the first of the three traditional requirements of a well-written sentence: clearness, force, and elegance. Those qualities are irresistibly appealing and they depend upon the right arrangement of elements to model their meaning.