There are several views to these theories.

Let me share with you the most simplistic explanation i've ever heard.

There are two ends of this scale.
One end is the kitten theory.
If you notice, when the mother cat picks the kitten up by the scruff of the neck, the kitten can kick and struggle all it likes, and it can't get away unless the mother puts it down.
It says that salvation is permanent, and no matter what you do, you're saved.

The other extreme is the monkey theory.
The baby monkey holds on tight to its mothers back, quite literally for dear life as the mother swings from tree to tree. If it ever lets go... it's humpty dumpty.
That theory says that salvation is dependant on the christian, that salvation can indeed be easily lost and you have to cling tight to it and hold fast, or else.

Most folk nowadays, balancing the two figure they'd stick to the kangaroo christian theory.
There's the pouch. You jump in and you stay in and the mother jumps around, and you're still in there, safe and sound.
Of course, if you jump out, that's your problem.
Salvation is a choice. It's not something you yourself earn and hold tight to. It's dependant on grace, on what He does and His providence (e.g. pouch). However, if you Don't Want It, and you decide to jump off the boat (or leave the pouch), then that's your choice as well.

It doesn't matter what these terms and terminology goes on and on about, or how much they're argued. Between these three theories, it's obvious that Jesus would not force salvation on anyone, and He wouldn't forsake you for what you do (you noticed that He CAME for those things, in the first place). So, I figure forget the terminology and theories, and just trust in Him.