if it was on air in 1986-1995, how come there are only 4 seasonS?

Because they are the years from which it began and ended. I believe the pilot episode went out in 1987 but the series wasn't commissioned until 1989, so then over those following years the 'seasons' were produced. Unlike America, a series of something isn't made to go out at alloted intervals, so it's not unusual to find gaps of sometimes a year or two between continuing series of a programme.

What's that? You just called me a bastard didn't you!

Wow, ender 'wiggen' sure asks some dumb questions.

As has already been explained, there wasn't a season/series every year, but sometimes there were 1 or 2 years in-between. I can imagine it would take some time to write enough material for an entire series, and since the show was based on sketches rather than a plot, there wasn't any need for any continuity. I also think both Laurie and Fry were probably busy working on other projects during that time.

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I was never that good at being nice when I should

British actors do a lot more than most American actors. They do t.v., stage, and movies all intermingled. Most British actors do t.v. when they are between other projects. With a few exceptions. Doing t.v. is almost like the off-season for them.

This is based on interviews I've seen w/ British actors explaining the phenomenon of British sitcoms.

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British shows do that sometimes, they take long breaks between seasons. Red Dwarf has released nine seasons over 22 years.

Cross my heart, smack me dead, stick a lobster on my head.