Technically, the axioms of consciousness and existence prove that there is consciousness, there is a reality separate from it, and that there is a link between the two (Perception).
What is so implausible about a disembodied brain? Perhaps a section of the solipsist’s mind has created the world and denies him conscious access to its true workings.
How can we be logical if our premises can not be trusted?
I don’t think you really can. We have to take the existence of the external world as an article of faith, or pragmatism, or suspended judgment, not as fact or rational belief.
One of the fundamental ideas in Objectivism is that everyone has a choice to believe what they want.
What choice is implied here? If an external reality, independent of the self, cannot be proven to any degree of certainty, isn’t suspended judgment the only tenable belief?
Were you floating in the sensory deprivation tank your entire life, and suddenly at some point, you conceived from nothingness the idea of numbers?
It’s difficult to even conceive of what existence as a disembodied brain would be like, much less to speculate on what it could and could not ascertain for itself. But if it had a sensation of being, and thought, already it has learned to count to two.
To refer to an essay by Rand on this - imagine Hellen Keller - blind and deaf from age 0.25, (3 months), without having yet developed the rudimentary concepts all of us functional humans take for granted such as the idea that words have meaning. It took months of her patient teacher tracing letters into Hellen’s palm while putting her other hand on something for Helen to get it: Words have Meaning. W-A-T-E-R means this wet feeling thing. (Only she didn’t even have a concept for wet at the time.)
But Keller must first have had a wordless conceptualization of the wet liquid thirst-quencher to even understand that it was a permanent and discreet phenomenon. Presumably that would be how the first proto-humans invented language, as well, by assigning categories to perceptions and sensations.
By definition (a different definition), the inductive inferential rule cannot be wrong.
But it can be. Tomorrow, the entropic arrow of time could reverse, the earth could cease spinning on its axis, and electrons could begin hopping out of their orbits like Mexican jumping beans. This does not contradict itself. But one measly square circle rends all fabric of meaning and existence.
And for that matter, by definition, any deduction with a universal quantifier which takes as a premise any proposition that is not previously proven by induction or any proposition which is not axiomatically given is wrong.
Or it becomes an existential quantification instead. Is the point that deductive logic ultimately requires axioms which are by nature self-justifying…?
The only way to defeat the evidence of the senses is to beg the question by asserting that the senses are necessarily invalid and indecisive.
Skepticism begs no question. Belief in the veridicality of the senses is affirmative, and establishes a burden of proof.