Soul

[Tex]

That's true.
If immaterial things do even exist, we can't test them directly.

But the other thing is that if we are to ever perceive them they have to interact with our known material universe to do so.

Let's just say for example, there is a guy standing right next to you but he exists in a 4th dimension of space.
You would have no way of directly perceiving him since you can't see in that dimension or "direction", even though he's right there.
They only way to have an indirect perception of him is if in some way or another he interacts with material in our dimension, which then can be measured and quantified. (Of course the problem with that is how do you determine it was an immaterial person, and not some as of yet unknown material cause?)

And of course the flip side is that if he never interacts with material in our dimensions, his very existence becomes irrelevant, since him not interacting with our material or him not existing are essentially the same thing relative to us.

I agree with everything here.