I did something last weekend I've never done before. Not once, but twice. I jumped out of an airplane. I went skydiving, a birthday present from my son.
Sure, it was thrilling to climb out of a Cessna 182 at 3,000 feet into an 80-mile-an-hour wind, hang from the strut, look back at my divemaster, who smiled and pointed her finger at me -- and let go, trusting my life to a bag of nylon and a bunch of cords. The serene beauty of the fields and forests surrounding Lake Wissota was breathtaking. And swooping down to the drop zone, pulling down on my toggles at 10 feet to flare the panels and stepping gently onto the blessed earth was as delicious as the first time I felt the intoxicating balance of a bicycle.
All that was grand. But what made the experience unforgettable was the six-hour training class, expertly taught by a club member. Of course, the other newbies and I were apprehensive, but we began to relax while I was hanging in the practice harness demonstrating the various positions we were to assume if we were about to hit a tree, building, car, cow or string of power lines. The drill gave us a lot of confidence.
That's when the instructor said, "Now, if both your main chute and your reserve fail, you'll gain a maximum velocity of 163 feet per second, or 111 miles per hour, in 9 seconds. At that speed you'll hit the ground in 22 seconds which rarely happens."
Then she hesitated. "Should there be a comma before my which clause?" she said, lowering her voice. "I never learned the rule."
It was an awkward moment. We all felt sorry for her. Naturally, everyone looked at me, perhaps because I was in the harness, or perhaps because they knew who I was from seeing my photo in the newspaper police reports. Before my classmates began to doubt our instructor's expertise, I spoke up.
"Yes," I said, in my most reassuring tone. "Use commas with which clauses that are parenthetical or nonessential, as in 'My reserve chute deployed perfectly, which was a good thing, since I inadvertently cut and released my main.' In that sentence, the clause, 'which was a good thing,' is nonessential. It could be removed without changing the meaning of the sentence."
"Thank you," said the instructor. "Such a simple rule. I'm embarrassed I didn't learn it in school. But how can I tell if the clause is essential or nonessential?"
"Simple," I said. "If you can place the clause in parentheses, use commas. If you can't, don't."
"Would you give us another example?" asked a fellow newbie, who like me was fit and trim.
"Sure," I said. "I used a comma before the nonrestrictive who clause in my preceding sentence."
"Now I get it," said the instructor. "Use commas with clauses that are nonessential; omit commas with clauses that are essential."
"Well done," I said, noting her comma-free essential that clauses.