Difference between ampersand (&) before or after command arguments

Question

I am a Windows user and I am using Cygwin as my terminal. In order to run notepad++ from terminal I have added this lines to ~/.bash_profile:

npp () {
    /cygdrive/d/Notepad++/notepad++.exe $(cygpath -w -- "$@")
    }

it worked, so next I needed a way to launch it on the background so I could open a npp++ instance without stopping my terminal flow. This worked:

npp foo &

But I did not want to introduce that ampersand manually, so I tried adding this alias to ~/.bash_profile:

alias npp="npp &"

And now:

npp foo

Works in the background.

The problem is that with gnu/linux commands you need to write ampersand after the arguments, if not it will not work.

this works:

ls directory &

This doesnt:

ls & directory

So I would like to know what am I missing here, because:

npp foo

Actually works in the background when I set

alias npp="npp &"

And it does not when I comment it.

Answer 1

The following command is launching in the background the ls executable passing directory as its single argument, this is what you want to do:

ls directory &

That one is launching ls in the background without any argument and then is (trying to) launch directory as a command in the foreground, this is not what you want to do:

ls & directory

Using an alias doesn't change this behavior, unless cygwin sh has a specific feature I'm unaware of, which I strongly doubt.