In meditation 4, Descartes begins to draw out the consequences of the existence of God for which he has argued in meditation 3. He has already indicated the first thing he wishes to establish, his principle that whatever he clearly and distinctly perceives is true. The basic idea here was stated at the end of meditation 3 when he notes that it follows from God’s perfection that he is not a deceiver. Meditation 4 can be seen as a more careful development of that idea. Much of the content follows that pattern of traditional treatments of the standard theological problem of reconciling God’s perfection and goodness with the imperfection of the created world. However, Descartes has as his focus a traditional philosophical problem, providing an account of error that reconciles its possibility with the possibility of knowledge. The meditation is short enough that we will be able to follow the steps of the argument fairly closely, so read it with that in mind.