Sceptics, fatalists, idolators, and atheists believe that matter exists unperceived. Scepticism results because we can't know if the perceived objects are like the unperceived objects. Ideas and sensations cannot exist unperceived. The RNS System continuously monitors brain activity at the implant site, unperceived by the patient. Knowledge through reason does not guarantee that there are, necessarily, unperceived objects. In fact the wound was deeper than it seemed, though unperceived at first.