Is there any way we can be sure that reality is as we perceive it through our senses, or that it is not an illusion that some third party imposes on us? I know that this subject was solved by Descartes, but I'd like to know is there any way of answering this question without an inate idea of God.
"Is there any way of answering this question without an innate idea of God?" Yes! I recommend starting with the detailed SEP entry on skepticism .