as such, on their own, per se, by themselves

Question

Which phrase in bold would you suggest to use? I hope it is clear what I am trying to say, but I am not sure about the word choice. Or perhaps I should use a different construction?

Also, I hope that I use the construction "not only ... but also" correctly here.

1. We will study discrete particle systems. They are not only of great interest on their own, but also represent an important intermediate step toward analysis of continuous systems.

2. We will study discrete particle systems. They are not only of great interest as such, but also represent an important intermediate step toward analysis of continuous systems.

3. We will study discrete particle systems. They are not only of great interest per se, but also represent an important intermediate step toward analysis of continuous systems.

4. We will study discrete particle systems. They are not only of great interest by themselves, but also represent an important intermediate step toward analysis of continuous systems.

Answer 1

(Native American English speaker here.)

They're all clear, they're all normal English, and it's nearly impossible to say which one is best.

These are also equally good:

They are not only of great interest for their own sake, …

They are not only of great interest for themselves, …

If you want some factors to consider in making a choice, which might also shed light on other word choices in other situations, here are some:

1. These days, it might not be a safe bet that your audience knows what per se means. For an academic audience, though, per se is fine. Note that since per se is Latin in the middle of an English sentence, it should be italicized in writing.

2. The meaning of “as such” is correct, but in this context it's less immediately clear than the other (all-English) versions. Other people may differ, of course. But I go through a moment wondering “as such what?”

3. An explicitly reflexive wording—“their own”, “themselves”—adds weight to the meaning you intend here, and probably makes the sentence clearer and easier to read.

Answer 2

Per se is Latin for by itself and is exactly identical in meaning to as such and by themselves. So I'm only going to compare the meaning between per se and on their own:

We will study discrete particle systems. They are not only of great interest on their own, but also represent an important intermediate step toward analysis of continuous systems.

Meaning: Discrete particle systems are of great interest without studying anything else, but the fact that they're an intermediate step toward analysis of continuous systems makes them even more interesting

We will study discrete particle systems. They are not only of great interest per se, but also represent an important intermediate step toward analysis of continuous systems.

Doesn't make sense (neither do the remaining two examples), this isn't how you use per se. Here's a correct example:

We will study discrete particle systems. They aren't of great interest per se, but they represent an important intermediate step toward analysis of continuous systems.

Meaning: Discrete particle systems aren't exactly interesting, but they become interesting when we consider the fact that they're an important intermediate step toward analysis of continuous systems.

Per se, as such, and by themselves should all be used in the negative. "They aren't interesting per se, but when we consider the following example they are interesting."

Answer 3

I believe the last one is the right one to use. 1- on their own is not appropriate to the subject discrete particle systems. 2- as such would mean as discrete. Is that what you mean ? 3- per se would have been right if the subject had been singlular. However,may be you should make a radical modification by saying : ... The subject is not of great interest in itself, but ... Hope this helps.