"Cogito ergo sum." These famous words from the philosopher René Descartes summarize his view, or maybe his thought experiment, on how we know. For Descartes, knowledge is knowledge if it originates in the thinker. Any knowledge that originates outside of the thinker must be doubted, questioned, examined, and reasoned by the thinker so as to make it knowledge that could have originated within the thinker. Until the knowledge originates in the thinker, it cannot be considered actual knowledge.
I am a Challenge III Director for Classical Conversations. My class of eight and I spend one day together per week going through all six academic subjects. Yesterday in Chemistry, we performed Experiment 3.2 from our textbook which uses a white sheet of paper and a red magic marker to experience the effects of rod and cone activity in the human eye.