With all the opposing ideas in the world, how do you know which ones are right? How do know your thoughts are any closer to the truth than someone else's? Are you sure you thought your thoughts through with absolute certainty? Before you think another thought, you need to know where to begin your thought. Where's that, you ask? Seventeenth-century philosopher Descartes suggests you begin by doubting. Continuing this study of philosophy and its consequences in our lives, Dr. Sproul teaches us about the age of rationalism and its effects in our own time as he looks at Descartes.