Question: There are many questions in philosophy of the following kind:

* Does my friend have a soul, or is my friend a zombie?
* Is the mind separate from the body, or is it the same?
* Where does the universe come from?

These questions have the property that, whatever the hypothetical answer would be, every one of your perceptions of the world is *exactly the same*.

It is a central tenet of Carnap and the positivists that one should consider such questions as meaningless, as an abuse of language. This position answers or moots most of the questions on this site. Positivism was accepted for a while in philosophy, but no longer. I am shocked by this.

Is it still considered correct that a question with no perceptible difference one way or another (like, "Are you a zombie?") is inherently meaningless? Why would anyone assign meaning to such a question?

Answer: 
I think that methaphysical theories (non testable in principle) are necessary and important to scientific research because they may be capable of becoming physical (testable in principle) theories.

Of course, if you understand clearly that your answers are completely equivalent experimentally, then you are saying just the same in different ways, you get into a purely formal ground, like when we state the equivalence of two different formulations of the same physical theory; but it may happen that the possible ways of showing the difference empirically are still not understood - think about the [Aharonov–Bohm effect](https://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect#Potentials_vs._fields), e.g.
**"no perceptible difference one way or another"**

To the senses, "no perceptible difference". To the intellect? **Profound** perceptible differences!

Nothing to be shocked about.