Our security guards are ever watchful and alert and ready for anything.

The meeting sped along with scintillating reports and analyses and presentations and discussions and motivational messages from the president and all five vice presidents and every departmental head.

Our hydrology group monitors area G which has been radionuclide free. [non-restrictive]

The weir control that was designed for low flow has been repaired. [restrictive]

The weir control which was designed for low flow has been repaired. [non-restrictive]

To calculate the flux from year to year we need complete, and accurate, data.

The supervisor could not make up his mind nor could he for that matter make up an excuse.

Punctuate to speed up:

Aside from last week's minor, radiation accident, we have had no trouble in the plant, or throughout the entire, International sweep, of installations.

Punctuate to slow down a little (allow reader some "breathing space" in which to absorb ideas):

Staff members in ERP and ESD have helped identify existing monitoring stations on the island but have not selected sites for the new stations nor helped visiting researchers from our sister lab in the Netherlands to assemble and place their equipment.

Punctuate to slow down a lot (increase the sense of "dragging":

The meeting dragged on with reports and analyses and presentations and discussions and motivational messages from the president and from each of the vice presidents and from every departmental head.

Punctuate to achieve medium emphasis:

First-aid boxes-located as usual to the left of welding stations-must be restocked regularly.

Punctuate to display balance:

It was the best time to invest it was the worst time to invest.

Colons
Use colons to

1. Introduce a list:

We need just three things from you: cooperation, trust, and money.

2. Introduce reasons:

The Oak Ridge Reservation is clearly an excellent choice for consolidation of the nation's plutonium production: it has an experienced national lab, a very secure facility, an abundant supply of water, and a supportive local community.

If you want to end the sentence with the line naming the Oak Ridge Reservation, for the rhetorical punch gained, you can recast the sentence to make the support (the reasons) precede the claim. You'll still want a colon:

To consolidate the nation's plutonium production at one site, we need an experienced national lab, a very secure facility, an abundant supply of water, and a supportive local community: the Oak Ridge Reservation is clearly an excellent choice.

3. Introduce illustrations:

Asthmatic patients can react to any kind of mammal dander: rabbits, for example, can be just as troublesome as cats.

4. Set off headers and notices of various kinds (like this one):

Note: pay close attention to details.
Warning: inattention to punctuation can ruin your style.
Remember: a colon says "namely," "the following illustrates my point," "for example," "as follows," or "note this."

Semicolons
Use semicolons to

1. Link two closely related sentences (especially sentences in cause-effect relationship):

Mercury levels in streams are alarmingly high; swift remedial action is needed.

The new digital cameras are the size of a credit card; wallets will soon bulge with them.

The company offered its stock at half price; consumers swarmed to buy it up.

2. Divide a single, long, main clause into readable chunks:

We took photos in the misty byways of London, the seamy underbelly of Paris, and the hot backstreets of Madrid; in the sprawling slums of Buenos Aires, the shivering outskirts of Lima, and the crowded streets of Mexico City; in the waterways of Hong Kong, the gardens of Kyoto, and the mud-bogged streets of Manila.

3. Divide a long sentence made up of multiple independent clauses:

Some species of animals, such as mink and otter, rank high on the scale of social value; other species, such as raccoon and beaver, fall somewhere around the middle of that scale; still other species, such as carp and skunk, nearly fall off the bottom of the scale.

When you have a string of independent clauses like this, it's always possible simply to come to a full stop (period) at the end of each clause. But sometimes, as in the sample sentence above, you want all the clauses in one sentence: it helps deliver the sense of one idea, one continuous "scale of social value," on which all animals fall.

Dashes
Use dashes to

1. Create a dramatic pause

The heron flapped in a wobbling ellipse above the belching smokestack and then fell to earth-stone dead.

The investors want to see our phone transcripts and email and memos and maps and sketches and figures and projections-immediately.

2. Add emphasis to a "parenthetical" element

These microchips-etched with the fate of humanity-control our nuclear weapons.

Note: dashes used this way are best regarded as existing on a scale of intensity or stress.
Consider this sequence:

These snail darters (the last of their kind) live only in Tellico River. light stress
These snail darters, the last of their kind, live only in Tellico River. medium stress
These snail darters-the last of their kind-live only in Tellico River. heavy stress
These snail darters-the last of their kind!-live only in Tellico River. very heavy stress

Again, it's true that you can also indicate levels of intensity by using italics, boldface, capitalization, or font variations of many kinds. Every now and then, it does make sense to take one of those options, especially italics, to create emphasis. But please hear me say "rarely." Just try, for example, sending to a good journal a piece of writing riddled with boldface, italics, capitalizations, etc. If the editors accept your article, it will come back to you marked up mercilessly, or with a note asking you to please remove all the noise. Yes, this happened to me. Once.

It's more effective-and more sophisticated-to use traditional punctuation marks. However, if you're determined to look amateurish, you can do it even with punctuation:

"These snail darters-the last of their kind!!!-live only in Tellico River."

I've illustrated one way to use punctuation for achieving different levels of emphasis, from lightest to heaviest. However, you could work a passage of prose so that the "whisper" of a parenthetical element actually draws attention and therefore "shouts"-in which case, we'd have to rank parentheses as capable of signaling heavy stress. What we're talking about here is rhetorical effect. Punctuation doesn't function all by itself in your rhetorical enterprise, of course. But skillful punctuation supports-sometimes, very significantly-your overall stylistic effort.

3. Show interruption or confusion:

"I'll try to turn off the electricity while you-" YEOW! screamed Fred.

The internal investigators-well, they are not precisely "internal," since they come from Washington, DC and have power to hire, fire, and completely reorganize any department here at the plant-have made their decision.

We didn't think-we had never supposed-it didn't seem possible to consider-that Russian engineers would be so careless with their reactor.

The tiny creatures-were they animals or plants?-moving towards the light-didn't that mean they were, at least, living things?-but we never found out.

Ellipses
Like dashes, ellipses can help you make your reader pause . . . then receive a following point with greater weight. Consider these sentences:

The incinerator engineers finally found the stored canisters of nerve gas . . . unfortunately, they didn't find them tightly sealed.

It's common to deliver some kind of irony or discovery or reversal of expectation after the ellipsis.

How about this sentence:

The sleepy corporal took the man's ID papers . . . slowly spread them out on his desk, yawning . . . then suddenly popped up and saluted.

The effect I wanted here was an image of this sleepy corporal taking his sweet time, not paying much attention to processing one more person through his checkpoint, and then realizing with a jolt that he was in the presence of a very important person. The ellipsis helps me out. It can be used as a "long dash" to cause the reader to slow way down. This creates a dramatic pause, at the end of which one delivers the punch.

Sure, I could write the "sleepy corporal" sentence using dashes, or even commas or parentheses, in place of the ellipses. But I wouldn't get quite the timing, and resultant jolt, I'm aiming for. I could also turn that single sentence into three separate sentences:

The sleepy corporal took the man's ID papers. He slowly spread them out on his desk, yawning. Then he suddenly popped up and saluted.

But this, too, would diminish the effect I desire. The short sentences give my narrative a quickness, an abruptness, that I don't want until the very end.

Exercise 2
Supply the missing colons, semicolons, dashes, and ellipses; remove the unnecessary ones. Substitute colons, semicolons, dashes, and ellipses for other pieces of punctuation where doing so seems to improve the sentence:

This hydrograph shows a similar trend a general decline in precipitation.

The opportunity opening up in Russia, potentially worth over a billion dollars to our company will not stay open long.

The bank clerk finally returned, carrying the safe deposit box, he opened it and we saw to our amazement that it contained nothing.

The mounting pressure of the river ice, slowly pushing up a glacier-like mound, the high winds, felling telephone poles and huge, ice-coated trees, the alternate snow and freezing rain (cutting down visibility to nearly zero) it was an onslaught of nature for which they were not prepared.

Two countries have agreed to grant us permits; Mexico and Colombia.

The two countries that have agreed to grant us permits, Mexico with its rampant crime and corruption and Colombia with its gangs and terrorists completely out of control are actually the countries hosting the best flora and fauna for our research.

After much hesitation, that is, after seeming to hesitate much, they delivered their verdict, guilty.