how is というなら different from なら?

Question

いい!? これからもし私たちが空へ行くというのなら....

is there any difference if i replaced it with なら? if there isnt, is there a sentence where it wouldnt be interchangeable?

Answer 1

Actually, all 行くなら / 行くというなら / 行くのなら / 行くというのなら are grammatically possible here. I mean, grammatically allowed but each has its own meaning.

• ～行くなら: if we (will / are going to) go...
  Yes, this is very straightforward. The non-past form tends to mean near future.

• ～行くというなら: under the condition that we go... / if you insist we go...
  V というなら is, in most cases, an idiom that means either of the following:

  1. "[an expression that tells it is okay/allowed] ... only if V"
  2. "if somebody insists to V"

  However, neither of them fits well in this context.

• ～行くのなら: if (there is) the fact that we go... / if the one (where) we go...
  の is a general nominalizer, accepting roughly two types of interpretation:

  1. apposition: "the fact of [predicate]"
  2. relative: "something or somebody that [predicate] / that is [predicate]-ed / with/to/from... which [predicate]"

  And if we take the former understanding, it yields the convoluted first translation above; but it is in turn, from a learner's perspective, combination of 行く + のだ + [conditional], which can be practically translated as "if we are bound/decided to go..."

• ～行くというのなら: if (there is) the fact that we say we go...
  The translation is even more enigmatic now :P, but here the point is that the extra という works in two ways. Firstly, it can eliminate the "relative" reading from bare V のなら to unambiguously mean the nominalization of the action. Secondly, it adds a little flavor of quotation という, which effectively introduces the nuance of subjunctive mood i.e. mentioning a hypothetical situation.

In conclusion, a cleaner answer would be like:

もし私達が空へ行くなら
if we go up into the sky

versus

もし私達が空へ行くというのなら
if we are supposed to go up into the sky
or
in the event that we go up into the sky

Answer 2

If you'd like to replace nami's sentence of 行くというのなら with 行くなら, the meaning is not changed much. Both 普通形(i.e. common type)（の）なら and 普通形なら can be used to give suggestion/advice.

But in my experience, the first one is often used to express a rather strong attitude, i.e. firm advice.