These are six meditations by the French philosopher Rene Descartes, best known for his conclusion "Cogito, ergro sum" "I Think, therefore I exist". They are called meditations because he clearly describes his deep reasoning on each topic. Each topic has objections made by Thomas Hobbs and Descartes' responses. The six topics are
Of Things Doubtful
Of the Nature of Mans Mind, and that ’tis easier Proved to Be then our Body
Of God, and that there Is a God
Of Truth and Falsehood
Of the Essence of Things Material, and herein again of God, and that He does Exist.
Of Corporeal Beings and their Existence, as also of the Real Difference between Mind and Body
(Summary by phil chenevert)