The Charvaka skeptics believed in perception, like the Vaisheshika and the Nyaya, but they did not believe in inference or theory of any kind. Not only did they believe in no gods or spirits or eternal soul, but they did not believe that the human mind can know things through inference but rather imagines simplified relations. This imaginary connection is an illusion. One can use inference as a tool, but it is always an imaginary illusion. Thus, they are agnostic about theory as well as theism. Only what is right in front of your eyes is real. This is very similar to Wittgenstein’s famous opening line of the Tractatus, the book that began modern truth table logic: “The world consists of facts, not of things”. The world may be real, but to us it is many imagined things and constructed facts, not a thing perceived directly. Thus, one can imagine and theorize that rain always requires clouds, but one cannot perceive all rain or all clouds or the connection between the two groups as a whole, and so one’s inference that rain always comes from clouds is an imaginary illusion, albeit a useful one to keep around.
Other schools criticized the Charvakas for failing to explain the origin of consciousness. The Charvaka reply was that consciousness was like the fermentation of alcohol. When one mixes several ingredients in the right proportions and gives it time, alcohol is produced. As such, consciousness is a temporary combination of elements that dissipates back into the material world from which it arose.