Why is Fringe S04E19 not the first episode of Season 5?

Question

We already know that episode 11 of season 2 was supposed to be air in season 1. That makes sense because they decided not to air it and finally changed their mind.

But I can't understand why they would air the episode that introduces season 5 in the end of season 4... it's not like the plot of season 4 and 5 have anything in common.

I'm only in the middle of season 5 so I may lack some information but here is what I understood so far :

Season 4 plot :

In the end of season 3, Peter "vanished from existence". In Season 4, he manages to reappear, but William bell and David Robert Jones (who are alive since Peter never existed... are you following ?) plan to destroy the world.

Season 5 plot :

The Observers have invaded the world. The Fringe Division is trying to destroy them.

The season 5 really is a Deux Ex Machina of the end of season 4, it is not a logical consequence

In the last minute of season 4, September suddenly appears and say "They are coming".He obviously speak about the Observers. This is the Cliffhanger to season 5.

But, again, no logical link between season 4 and 5.

So... Why was episode 19 of season 4 not aired as the first episode of season 5 ?

Answer 1

It's part of the structure of Fringe's seasons. In the 19th episode of the first four seasons, they do something that's off the beaten path compared to the usual Fringe episode:

• S01E19, The Road Not Taken, the show's mythology is massively fleshed out. It's established that there is another universe, and that Olivia is able to access it. This episode also establishes that the children in the Cortexiphan trials are still out there, and being used by ZFT. All of this is later developed in Season 2.
• S02E19, Brown Betty, was a musical episode.
• S03E19, Lysergic Acid Diethylamide, was the episode where the team goes into Olivia's mind. Some of the segments in her mind are animated.

With S04E19, they do this by suddenly showing us a dark future that had been foreshadowed.

Answer 2

I wouldn't say Season 5 was entirely disconnected - The Observers were a series-long plotline that had yet to be resolved, which had been steadily building. Especially with 4x14, The End Of All Things. They needed to resolve it somehow for the series to really feel complete.

That said, as the end of Season 4 approached, I recall there being fears that the series would not be renewed, as it had started to drag on, especially with how Season 4 started. Episode 4x19, Letters of Transit, was used as an extended teaser to keep interest high so that it could get renewed just one more time, and the series could be given a resolution.