If he isn't here, he's sick.
If he isn't here, he isn't feeling well.
If he doesn't know the answer,
he admits it.
If he doesn't know the answer,
he doesn't admit it.
If they aren't here, we'll miss them.
If they aren't here, we won't miss them.
If they don't attend the meeting,
I'll be surprised.
If they don't attend the meeting,
I won't be surprised.
If he weren't here, we'd call him.
If he weren't here, we wouldn't call him.
If he didn't know the answer,
he'd admit it.
If he didn't know the answer,
he wouldn't admit it.
If he hadn't been here, we would've
called him.
If he hadn't been here, we wouldn't have
called him.