Reason Not The Only Source of Knowledge

Is irrational just "false" or is there something else to it?

There’s more to it.

Are there true but irrational ideas?

I don’t think so, no.

I think rational but false ideas must exist, no?

Yes. Mere falsehood does not imply irrationality.

Okay I read it. Not sure I'm clear on my questions after doing so to be honest.

You asked if rationality was just false or if there was something else to it. Note that the word ‘false’ does not occur on the linked page. Instead, she mentions the destruction of life, dishonesty, lack of integrity, context dropping, the rejection of mysticism, and more. These are attitudes toward truth seeking and their effects.

You asked whether rational but false ideas must exist. That is what Rand means by “not blindness, but the refusal to see, not ignorance, but the refusal to know.” Blindness = being wrong on some issue, refusal to see = refusing to seek or recognize the truth on some issue. To her, blindness and the refusal to see are not the same thing, which answers your question.

If I get her right, one could in principle hold a rational belief which is false —a belief in god, say— so long as this belief stems from a sincere effort to explain the world and so long as the believer is ready to jettison his belief if he were to think of some reason why it cannot be true.