They do different jobs.
In this sentence:
So the sentence is structured like:
This pattern is very common in Japanese:
Literally, 匂いがする means something like:
So:
Here, する is not the usual to do in the sense of performing an action yourself. In expressions like this, it means something more like to be sensed or to give off.
Common similar patterns are:
いい and よい both mean good.
In modern Japanese, いい is much more common in everyday speech. So いい匂い is the normal, natural phrase for a nice smell.
You may still see よい in:
For example:
So いい匂い is exactly what you should expect here.
Not necessarily.
匂い just means smell or odor in a general sense. Whether it is pleasant or unpleasant depends on context.
Also, Japanese has a nuance difference:
So in this sentence, the adjective いい tells you clearly that it is a pleasant smell.
Yes, it can be written in kanji as 石鹸.
However, in modern Japanese, this word is very often written in kana:
Kana is common because:
So 石けん is a very normal spelling.
します is the polite -masu form of する.
So:
That means the casual version of the full sentence is:
この石けんはいい匂いがする。
You would use:
Yes. That is also natural.
Both can mean roughly This soap smells nice.
The nuance is slightly different:
In many situations, the difference is small, and both are fine.
The basic order here is the natural one:
この石けんは いい匂いが します。
Japanese is more flexible than English, but particles show the role of each part, so the particles matter more than the exact position.
Still, not every rearrangement sounds equally natural. For learners, the safest pattern is:
Examples:
So yes, Japanese has some flexibility, but this sentence is already in a very standard order.
A helpful breakdown is:
So the structure is:
That literal meaning becomes natural English as:
This is a good example of how Japanese often expresses sensory ideas indirectly, using patterns like 音がする, 味がする, and 匂いがする.