By Bill Ward

Adults cruising along on their keyboards provide a small source of amusement with their misuse of certain basic principles of grammatical structure. A few months ago, I was involved on the Internet in a discussion about one of those principles. It arises from confusion about the use of the words that and which.

First, are they interchangeable? Simple answer: No, because they indicate different things.

“That” is restrictive. What does restrictive mean? “That” introduces a phrase that is essential to the meaning of the work it modifies. The phrase is not set off with commas, or, you might say that all parts of such a sentence are joined at the hip. One part can’t function without the other.

Example:  We purchased software that provided all the necessary features.

“Which” is nonrestrictive, meaning that “which” introduces a phrase not essential to the meaning of the word it modifies. The phrase is set off by a comma behind “which.”

Example:  We purchased software, which provided all the necessary features.

My car does a quarter-mile in 4.5 seconds, which is not the speed I hoped to reach.

The ends of the last two sentences, set off by “which,” are of questionable relevance, and you can remove them, if desired.

Salisbury, being ‘a’ or ‘an’ historic or historical (?) town, contains a lot of old buildings, some of which may be deemed as just downright old, or others perhaps, historic. But as we started off, are they historic or historical?

So, I decided to refer the question to one of the best grammar experts I know of, the late James J. Kilpatrick. To do that, I went to my files and found Kilpatrick’s writing from March 2004.

He recommends exploring the differences by example rather than fumble with explanations. He thought Charleston was the South’s most historic city. And the Supreme Court’s decision in Brown v Board of Education was an historic decision.

“Historical” means “having to do with history.” That explains why many historical publications have carried articles on Ft. Sumter.

This is a simple test:  Try “famous” and see how it works. If something is famous, then you’d call it “historic.” And famous decisions, moments, turning points and matches were historic. On the other hand, we’re not likely to find famous correlations, data or facts.

It was interesting to note that as demanding as he was about grammar, Kilpatrick used the incorrect spelling for the Civil War ironclad, USS Merrimack, also improperly called the Merrimac. It’s an easy error to make.  In Massachusetts, the Merrimack River flows through the town of Merrimac.

That’s enough of the spelling lesson. Let’s decide if the Merrimack was “an” historic ship or “a” historic ship.

An old rule of thumb was to use “an” before words beginning with a vowel and “a” before words beginning with a consonant — such as an apple, a carrot, an icon, a model. But that rule has long since gone by the wayside. Vowels and consonants no longer control your choice of “a” and “an.”

The choice is practically always controlled by the sound of the syllable it modifies. But unfortunately, the sound rule can fade when challenged with conflicting pronunciations.

Some standard references, such as the Associated Press Stylebook, can be too simple: “Use the article ‘a’ before consonant or hard sounds; use the article ‘an’ before vowel or soft sounds.”

The New York Times demands “a hotel” and “a historical.” Henry Fowler, of Fowler’s Modern English Usage, can often use sharp criticism on various issues. However, he was tolerant on this, saying that in many cases, the choice is “the sort of thing about which we ought to be allowed to do as we please, so long as we are consistent.” Go figure.

Bill Ward is an MIT-trained writer and editor. He has taught technical writing and editing for adult professionals at Queens University in Charlotte. Contact him at wardwriters@carolina.rr.com .