And. Then. And then. Those three, simple, insignificant parts of speech drive many writers to the nut house, and give editors fits. You'd think something so small wouldn’t have such a large effect on people. But they do.

Here’s a sentence to get you thinking:

Joe opened the door and walked out into the hall.

Now what is wrong with that sentence? We speak like that, don’t we? I’m going to bet you visualized Joe opening the door. Joe stepping through the doorway. Joe standing in the hall.

Unfortunately, that isn’t what the sentence said.

The word “and” when not partnered with the word “then” means the same thing that it does in math. Combine two things. In math, we combine numbers (or numerical placeholders). When we say 1+1, we mean 1 and 1. More than that, when we say 1+1 or 1 and 1 what we are also saying is “2”. (Which is why we can say 1+1=2 or 1 and 1 equals 2).

With the basics established, let’s go back to Joe and his attempt to get out into the hall. To see what is happening to him in our original sentence, we’re going to write it as a math formula, thus:

Joe opened the door + walked out into the hall = one bumped nose

What happened is that Joe both tried to open the door AND walk out into the hall at the same time. Unfortunately, most people, Joe included, just can’t walk through solid objects. Thus he now has a bumped nose.

What we should have written is
Joe opened the door AND THEN walked out into the hall.
Because that’s really what we meant.

To make it simple when writing, think “sequence of events.” Do the events all happen at the same time? If not, what order to they happen in?

If they all happen at the same time, use “and”. If they happen one after another, you have to stick that “then” into the sentence.

And that bring us to:

“And then” as opposed to “then”

When should you use the “and then” phrase instead of just the word “then”?

Here’s something to practice on

Joe walked down the hall. Joe turned the corner.

In order to smooth out the flow, we really need to connect those two sentences. But do we connect them with and, and then, or then?

Referring back to the section above, it’s pretty obvious that Joe isn’t going to be walking down the hall AND turning the corner at the same time, so “and” by itself is out. That leaves us with “and then” or “then”

Again, think in terms of math. We are adding two actions together, so we need that “and”, but we aren’t doing them at the same time, so we need that “then”. That gives us

Joe walked down the hall, and then turned the corner.

But why couldn’t we just say

Joe walked down the hall, then turned the corner

We could, but if you’d like to save your editor a few grey hairs, it would be best not to. Unless you’re writing dialog. In dialog, all the rules are thrown out. Dialog should be written the way the character in question speaks. But in narration, good grammar is important. (The exception is narration written in 1st person… because everything in a 1st person story is technically dialog. Either dialog being said to the reader or dialog in quotes being said to other characters.)

So when do we use “then” all by itself?

It’s useful in a sequence of objects such as:

The water turned green, then orange, then red, then yellow, the vanished completely.

It works well for connecting a consequence to an action:

If you are late for work, then you will be fired

It’s a nice bit of extra wordiness when you need to sound pompous, or you’re writing a travelogue:

This, then, is where the last of the settlers fell after they foolishly annoyed the fire-ant mound.

There are plenty of places to use “then” all by itself. there are plenty of spots where “and” doesn’t need a partner, and there are many occasions when they work well together.

Just remember, the next time you pull down your pants and go to the bathroom, the addition of one extra word would have kept you from having to do laundry.

For more writing tips, see also "How to write a query letter".