When we say that the conventions of language are logical (indeed, that they must be logical), we are asserting that these conventions have not come about arbitrarily. If that were the case, they wouldn't have survived. Conventional usage is a long-term answer to the problem of communication, not a short-term whim. We may not know the roots of a conventional practice, but it is usually possible to understand its logic.

As an example, consider the use of the apostrophe in English. Millions of people are apparently baffled about when and how to use the apostrophe, as if the whole matter were determined by some advanced linguistic calculus understood only by people with doctorate degrees in linguistics. However, the apostrophe has only two functions –to mark possessive nouns and to mark a contraction.

Common sense and logic tell us when a noun is possessive – when it denotes ownership or something akin to ownership. Then, since we use the sound of the letter s both when a noun is plural and when it is possessive, we need a way to distnguish between a possessive noun and a simple plural. The rules give us a logical way to do that. All we need to do is to go back to the "owner word" (the noun that is possessive in sense) and modify it according to these rules. The only possible confusion should be when the noun in question does not express literal ownership (usually a noun denoting a period of time or sum of money). For example, in "a week's pay," the week does not literally own the pay, so possessive case seems illogical. However, it is even more illogical to have "a weeks pay" because a [designating one item] + weeks [designating more than one] doesn't make sense.

As for the use of the apostrophe in contractions, nothing could be simpler or more logical. Here the apostrophe represents an omitted letter (or letters) when two words are combined into one. If people cannot distinguish between its and it's, it's not because they language is logical but because they aren't using logic. The apostrophe in it's obviously represents the omitted i from is when we combine it and is. Thus, it's means it is. That's (That is) hardly a huge feat of logic. By logical deduction, therefore, it's is not the possessive form of it, nor does its mean it is. (Though it's helpful to know that personal pronouns do not form the possessive by adding 's, we don't need to go any further to understand the distinction – unless, of course, we want to explain how the language is logically consistent in the treatment of possessive pronouns versus possessive nouns.)

Logic governs punctuation. The placement of commas (which seems a mystery to many people) is altogether logical if one understands the way sentences are structured. For example, since subject—>verb should represent a flow of thought, we never put a single comma between the subject and the verb. If there is an interrupter of some sort between the subject and the verb, we need two commas – one representing the beginning of the interruption, the other representing its end.

We can also, to some degree, determine logically where punctuation marks go (and what punctuation marks to use) by observing the rhythm of the language. A comma is a brief pause, a dash is a longer pause, a period is a stop, and a semicolon is also a stop but a less abrupt one than a period. Exclamation points and question marks should be self-explanatory. People have difficulty with punctuation marks not because punctuation is illogical but because they are inattentive to the natural rhythms of the language. People who read badly when they read aloud are often ignoring the punctuation marks, and that is why their reading sounds unnatural. (There have been, by the way, many questions on this site's Grammar Discussion Board that the questioner could easily have answered by applying simple logic.)

When people have difficulty with commonly confused words, it isn't usually because the distinction between these words is illogical. It is because they don't pay enough attention to how the language works logically. To take one example, there's no logical reason for confusing there and their if one understands how the logic works. Their is formed by taking the pronoun they and changing the y to ir, thus forming a possessive pronoun, which bears no logical relationship to the adverb there. The two words may sound the same, but that's as far as the similarity goes. Their also illustrates a pattern among possessive pronouns. Each has its own way of showing possession. It is, to be sure, a frustratingly irregular pattern and must be learned (unlike with possessive nouns, where the pattern can be reduced to a rule). However, we can at least say, "Oops, pronoun – proceed with caution."

Verbs exhibit a similar mix of perfect logic and irregular exceptions. The regular verbs can be conjugated according to rules that govern all of them, and the vast majority of the verbs in our language are regular. Irregular verbs, like the personal pronouns, cannot be conjugated according to any overarching rule because they are . . . well . . . irregular. They must be learned individually. Making our way from be to is, are, was, and were is not something we can do by a global equation but something we must learn. Nevertheless, as noted in Part 1 of this series, exceptions and irregularities do not prove that the enture language is devoid of logic.

If we note the complexity of language and declare it to be therefore illogical, we are being illogical ourselves. Is it logical to take something as complex in form and function as language to be simple? That's a bit like expecting all colors to be only the primary colors, without any shades. Everything would be red, orange, yellow, green, blue, indigo, or violet. There would be no purple, orange, pink, maroon, or aquamarine. Language is not only complex but derives much of its "color" from that complexity. That doesn't make it illogical.

I always tell my students not to expect the English language to be perfectly logical, and I sometimes have fun with it by demonstrating how illogical it can be, especially with respect to spelling. On the other hand, I spend a considerable amount of time showing how they can master the grammar of English by understanding the logic behind the rules. It's possible to reinforce this point by demonstrating that many of their errors with grammar are also violations of logic ("one days pay" is not just a violation of the rule governing the possessive case; "one days" is also blatantly illogical). In short, we cannot master the language by logic alone, but the use of logic certainly helps.