I have a very good reason for offering this book to you, and I am confident that you will have an equally good reason for giving it your protection once you understand the principle behind my undertaking; so much so, that my best way of commending it to you will be to tell you briefly of the goal which I shall be aiming at in the book.

I have always thought that two topics – namely God and the soul – are prime examples of subjects where demonstrative proofs ought to be given with the aid of philosophy rather than theology. For us who are believers, it is enough to accept on faith that the human soul does not die with the body, and that God exists; but in the case of unbelievers, it seems that there is no religion, and practically no moral virtue, that they can be persuaded to adopt until these two truths are proved to them by natural reason. And since in this life the rewards offered to vice are often greater than the rewards of virtue, few people would prefer what is right to what is expedient if they did not fear God or have the expectation of an after-life. It is of course quite true that we must believe in the existence of God because it is a doctrine of Holy Scripture, and conversely, that we must believe Holy Scripture because it comes from God; for since faith is the gift of God, he who gives us grace to believe other things can also give us grace to believe that he exists. But this argument cannot be put to unbelievers because they would judge it to be circular. Moreover, I have noticed both that you and all other theologians assert that the existence of God is capable of proof by natural reason, and also that the inference from Holy Scripture is that the knowledge of God is easier to acquire than the knowledge we have of many created things – so easy, indeed, that those who do not acquire it are at fault.

So serious are the doubts into which I have been thrown as a result of yesterday's meditation that I can neither put them out of my mind nor see any way of resolving them. It feels as if I have fallen unexpectedly into a deep whirlpool which tumbles me around so that I can neither stand on the bottom nor swim up to the top. Nevertheless I will make an effort and once more attempt the same path which I started on yesterday. Anything which admits of the slightest doubt I will set aside just as if I had found it to be wholly false; and I will proceed in this way until I recognize something certain, or, if nothing else, until I at least recognize for certain that there is no certainty. Archimedes used to demand just one firm and immovable point in order to shift the entire earth; so I too can hope for great things if I manage to find just one thing, however slight, that is certain and unshakeable.

I will suppose then, that everything I see is spurious. I will believe that my memory tells me lies, and that none of the things that it reports ever happened. I have no senses. Body, shape, extension, movement and place are chimeras. So what remains true? Perhaps just the one fact that nothing is certain.

Yet apart from everything I have just listed, how do I know that there is not something else which does not allow even the slightest occasion for doubt? Is there not a God, or whatever I may call him, who puts into me the thoughts I am now having? But why do I think this, since I myself may perhaps be the author of these thoughts? In that case am not I, at least, something? But I have just said that I have no senses and no body. This is the sticking point: what follows from this? Am I not so bound up with a body and with senses that I cannot exist without them? But I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I too do not exist?

During these past few days I have accustomed myself to leading my mind away from the senses; and I have taken careful note of the fact that there is very little about corporeal things that is truly perceived, whereas much more is known about the human mind, and still more about God. The result is that I now have no difficulty in turning my mind away from imaginable things and towards things which are objects of the intellect alone and are totally separate from matter. And indeed the idea I have of the human mind, in so far as it is a thinking thing, which is not extended in length, breadth or height and has no other bodily characteristics, is much more distinct than the idea of any corporeal thing. And when I consider the fact that I have doubts, or that I am a thing that is incomplete and dependent, then there arises in me a clear and distinct idea of a being who is independent and complete, that is, an idea of God. And from the mere fact that there is such an idea within me, or that I who possess this idea exist, I clearly infer that God also exists, and that every single moment of my entire existence depends on him. So clear is this conclusion that I am confident that the human intellect cannot know anything that is more evident or more certain. And now, from this contemplation of the true God, in whom all the treasures of wisdom and the sciences lie hidden, I think I can see a way forward to the knowledge of other things.

To begin with, I recognize that it is impossible that God should ever deceive me. For in every case of trickery or deception some imperfection is to be found; and although the ability to deceive appears to be an indication of cleverness or power, the will to deceive is undoubtedly evidence of malice or weakness, and so cannot apply to God.

[The cause of error]

You say that although you have no power to avoid error through having a clear perception of things, you can still avoid it by firmly resolving to adhere to the rule of not assenting to anything which you do not clearly perceive. But although you can always keep this rule carefully in mind, is it not still an imperfection not to perceive clearly matters which you need to decide upon, and hence to be perpetually liable to the risk of error?

You say that error resides in the mental operation itself in so far as it proceeds from you and is a kind of privation, but not in the faculty God gave you, nor in its operation in so far as it depends on him. But although the error does not immediately reside in the faculty God gave you, it does indirectly attach to it, since it was created with the kind of imperfection which makes error possible. Admittedly, as you say, you have no cause for complaint against God who, despite owing you nothing, bestowed on you the good gifts which you should thank him for. But there is still cause to wonder why he did not bestow more perfect gifts on you, given that he had the knowledge and the power and was not malevolent.

You go on to say that you have no cause to complain that God's concurrence is involved in your acts when you go wrong. For in so far as these acts depend on God, they are all true and good; and your ability to perform them means that there is, in a sense, more perfection in you than would be the case if you lacked this ability. You continue: ‘As for the privation involved – which is all that the essential definition of falsity and wrong consists in – this does not in any way require the concurrence of God, since it is not a thing and should not be referred to him.’ But although this is a subtle distinction it is not quite enough to resolve the problem.

[The rejection of previous beliefs]

[It is objected that] I am asking for something impossible in wanting us to give up every kind of preconceived opinion … But [my critic] has not realized that the term ‘preconceived opinion’ applies not to all the notions which are in our mind (which I admit it is impossible for us to get rid of) but only to all the opinions which we have continued to accept as a result of the previous judgements that we have made. And since making or not making a judgement is an act of will (as I have explained in the appropriate place) it is evident that it is something in our power. For, after all, in order to get rid of every kind of preconceived opinion, all we need to do is resolve not to affirm or deny anything that we have previously affirmed or denied until we have examined it afresh. But this does not entail that we cease to retain all the same notions in our memory. Nevertheless, I did say that there was some difficulty expelling from our belief everything we have previously accepted. One reason for this is that before we can decide to doubt, we need some reason for doubting; and that is why in my First Meditation I put forward the principal reasons for doubt. Another reason is that no matter how much we resolved not to assert or deny anything, we easily forget our resolution afterwards if we have not strongly impressed it on our memory; and this is why I suggested that we should think about it very carefully. [Appendix to Fifth Objections and Replies: CSM II 270]

Here I shall employ an everyday example to explain to my critic the rationale for my procedure, so as to prevent him misunderstanding it, or having the gall to pretend he does not understand it, in future. Suppose he had a basket full of apples and, being worried that some of the apples were rotten, wanted to take out the rotten ones to prevent the rot spreading. How would he proceed? Would he not begin by tipping the whole lot out of the basket?