A lot of beginning writers have difficulty with the difference between simple and continuous tenses. Once you understand the purpose of them, though, there's really no difficulty.
Starting with the past tense, as the distinction is the most readily apparent, let's consider the operation of simple and continuous past tense.
PAST SIMPLE: Rover ate a bone.
PAST CONTINUOUS: Rover was eating a bone.
In the simple past
tense, the action described is complete. The entire action of Rover eating the bone all
happens within the confines of the sentence. At the beginning of the
following sentence, he has finished eating it. Of course, you might go
on and describe him eating it, but that's in the nature of a recap
(Rover ate the bone. He went at it like a mad creature, tearing and
slobbering.) In the most simple narrative, the next sentence moves on in
time. (Rover ate the bone. Then he had a big drink out of the water
bowl.)
In contrast, in the continuous past tense, the action described is
ongoing. At the end of the sentence, Rover is still eating away at that
bone.
Thus we may see that the continuous past tense is used to describe a state of affairs. For example:
When I walked into the kitchen (simple past; action completed) I froze in horror. (simple past; action completed)
Rover
was eating the Sunday roast, all over the floor. (see the difference?
This is telling you what is now going on, and it's still happening).
Fluffy was in the corner, vomiting. (again, she's still golloping away).
Now let's apply
this to the present tense. As with the past tense, there are two forms
of it.
PRESENT SIMPLE: Fluffy kills a seagull.
PRESENT CONTINUOUS: Fluffy is killing a seagull.
In the present
simple, the action, again, is complete. At the end of the sentence that
is an ex-seagull. It has ceased to be. Only a carcass remains.
In
the present continuous, what we have is a point-in-time snapshot.
Fluffy is killing a seagull. Right here, right now, this is what's
happening. Help! Get the broom! He's killing it! You still might save it
if you act quickly because the act of killing is NOT COMPLETE.
A good rule is always to use the simpler form when it
does what you want, reserving the more complex form for when the simple
one doesn't work.
EG: I walk into the room. Rover eats the Sunday roast.
See
how that completely doesn't work? Here, we are saying that Rover eats the roast, commencing his depredations only after you walk into the room. The two
sentences look disconnected and weird.
I walk into the room. Rover is eating the Sunday roast.
See the difference? OMG what's he doing, that I JUST CAUGHT HIM AT!
This same distinction applies to every tense. A rule
of thumb is that whenever you have the participle (eating, opening,
whatever, things ending in -ing) you have a CONTINUOUS action. It is the same
in the future.
EG: When you next see me, I will drink coffee. (I will
have a coffee with you even though I have not been doing so).
When you
next see me, I will be drinking coffee (I will be slugging down the
black stuff at the moment you walk into the cafe).
