[pmoriarty]

"Solipsism is basically the only defense against the conclusions from the evidence of the "real" world."

Far from it. There could very well be an external world, and one populated by plenty of other and fully real human beings even, but your own personal view or understanding of it could be distorted or false.

This could be simply because you're hallucinating, or insane, or your brain could be injured, or could be living in a virtual reality (which itself exists in some other "real" reality), or you could be the proverbial brain in a vat, or aliens (or god or a demon/devil) could be deceiving you, etc.

[redial]

All those options are the same: they are either part of a shared experience or they are not. Nothing is preventing a demon from deceiving me right now, in fact one can come anytime I'd love to meet him, preferably her.

[pmoriarty]

If experiencing something that's not shared is the only qualification for solipsism, then we're all solipsists, as (arguably barring the possibility of telepathy) our experiences are all private.

But that's not what solipsism typically means. Solipsism usually refers to the position that only you (or perhaps only your own mind) exist. By that commonly accepted definition, one could be mistaken or deceived in any of the ways I laid out earlier without them entailing solipsism.

[redial]

I meant to say shared context. Everything you said is part of a shared context or not, those are the only two options.

[pmoriarty]

Even if there is some sort of "shared context" (more commonly known as "objective reality") your view or understanding of it could still be deceived, hallucinating, simply mistaken, insane, etc. These are not solipsism. What they are are possible obstacles to your connection to any shared context or objective reality.

[redial]

Sure, but they don't change the fact those are the only 2 options.

And in the "shared reality" option, consciousness is somewhat measurable.