Sense-data can be relied upon, since it is the only thing we have, whether matter exists or not. Systematic doubt - a method invented by Descartes [1596-1650) - is a philosophic method which says that one should doubt everything and believe nothing that one cannot see clearly and distinctly to be true. l think, therefore I am ' (3033130, ergo sum; no matter what may be, one can be sure of one's own existence if one can doubt. Sense-data cannot be dismissed entirely: If the table is a product of one's sense-data and one covers the table with a piece of cloth, is the table now non-existent and the cloth is suspended in empty air? Since there are things that continue to exist even if we are not perceiving them - say, a cat that changes its position from one place to another or gets hungry after an interval of time, regardless of if we observe it or not - one can reasonably assume that there are things independent of our senses. Philosophy should focus on ordering our instinctive beliefs, beginning with those we hold most strongly, into a hierarchy. It shouid take care to show that our instinctive beliefs do not clash but form a harmonious system. The possibility of error is diminished by the interreiation of those instinctive beiiefs and by critical scrutiny which precedes acquiescence of knowledge