The empiricist philosopher John Locke worked out some of the details of an important distinction (originally formulated by Descartes) between primary and secondary qualities, and he was quite pleased with himself as this distinction allowed for the possibility of doing some serious science: you can't study secondary qualities objectively, since they are essentially subjective (and thus liable to change from person to person), but you can study primary qualities scientifically, since there is no difference in those cases between what you experience and what is.As you can learn in the following hilarious little presentation, little did Locke imagine that soon after, a) Bishop Berkeley would take this distinction to its logical conclusion and show that there is no real difference between primary and secondary qualities, and that b) the physical world would disappear as a result...
Esse est percipi... Dang!