Ask the Christian

[lucent]

Ah, but you do gain evidence to corroborate your suspicions that there is something beyond your mind in the various individuals who confound you by doing things directly to contradict your will and desire. The solipsist argument will not help you here, because, if it holds water, you must abandon your god first and foremost as being the character most unlikely to exist. Whereas there are other beings who should at least "seem" to exist for you (discoverable by means of your five senses), your god is not discoverable by any of these senses. So if you wish, apply the Cogito in that direction: Cogito ergo (deus) non est.

Obviously the external world cannot serve as proof for the external world.

Exploring your claim though, the belief that there are minds other than my own is something else which cannot be proven and that I choose to believe. This again shows the original claim to be false.

I don't have to abandon anything, by the way. I am simply proving that the claim "it is irrational to have a belief without sufficient proof" is false, and self-refuting.