嘘をついているのではないかと疑った。

Question

私は彼が嘘をついているのではないかと疑った。

The amount of particles used here confused the shit out of me and I couldn't understand anything so I need help understanding what each particle does here. Why not just say 私は彼が嘘をついているので疑った。 Or 私は彼が嘘をついていると疑った。

Answer 1

Why say it longer?

The longer expression is longer, and includes more and different information. :)

Analyzing

Breaking it down:

• 私は彼が嘘をついているのではないかと疑った。

The topic goes with the ending verb here:

• 私は...と疑った。
  I suspected [that] ...

That's pretty straightforward. 疑う is like 思う, in that the thing you're suspicious about, or thinking about, takes the particle と. This is similar to the use of "that" in English, as in "I think that..." or "I suspect that..."

So let's look at the bit in the middle:

• 彼が嘘をついているのではないか

We've got a basic statement, and then a bunch of stuff on the end.

• 彼が嘘をついている
  He is telling a lie

That's pretty straightforward too.

• のではないか

The のではないか on the end is a common way of speculating about something: "isn't it [whatever came before]...?" In other words, "I think it's probably [whatever came before]." In common informal speech, のではないか shortens to んじゃないか. When talking with someone else and seeking confirmation, sometimes speakers will omit the か and express the question using a rising tone of voice. You might have heard んじゃない? in conversation or media.

Putting the middle back together, we get:

• 彼が嘘をついているのではないか
  He is telling a lie, isn't he

Then, putting the middle back into the full sentence, with tense and other grammatical adjustments:

• 私は彼が嘘をついているのではないかと疑った。
  I suspected that he was probably lying.
  (Alternatively) I thought, "he's lying, isn't he?"

Why not say it shorter?

We could say it shorter, and more directly, as you suggest:

• 私は彼が嘘をついていると疑った。
  I suspected he was lying.

It's the same general idea, but it leaves out important color by omitting the speculative overtones inherent in のではないか.

One of your suggested renderings doesn't quite work:

• 私は彼が嘘をついているので疑った。
  I suspected, because he was lying.

This changes the meaning substantially, and goes in a different direction from the original. It's also not clear anymore what 私 suspected, only that 私 suspected it because 彼 was lying.

HTH!