Meditations - pg. 104

For there is indeed no necessity for me ever to happen upon any thought of (cogitationem de) God; but whenever I choose to think of (cogitare de) the First and Supreme Being, and as it were bring out the idea of him from the treasury of my mind, I must necessarily ascribe to him all perfections, even if I do not at the moment enumerate them all, or attend to each. This necessity clearly ensures that, when later on I observe that existence is a perfection, I am justified in concluding that the First and Supreme Being exists.