Networks emerge and evolve as actors (people, organisations, groups, etc.) continuously form, dissolve or change ties and, as they learn, accumulate experience and change their characteristics. In understanding network dynamics it is important to distinguish between network change and network evolution. Network evolution refers to the changing dynamics of the network over time as a result of an understood process (Doreian and Stokman, 1997). Whereas Chapter 12 focused on the micro-processes of tie formation, network evolution is a globally observed macro-process. In this chapter, network evolution refers to processes that drive network change from the bottom up, without any coercive or directive mechanisms that act upon networks from the top down.

It is not possible to arrive at universal rules of network evolution, because of the diversity of networks involved in innovation. Sectoral dynamics, regulations and institutions influence network evolution differently across contexts. At the same time, it is possible to observe certain structural regularities across different types of networks. There is certainly a path-dependent dimension in network evolution, where past networks shape future networks. But there are other external factors as well, those which can alter the structure of a network in a radical and unforeseen manner.

As a network evolves its structure may change or remain (more or less) the same. Ties are formed (or dissolved) continuously, so it is highly unlikely that an innovation network will stay the same, even for a short time. Therefore it is better to think in terms of the extent to which change diverges from the existing structure. For example, when a network with many clusters grows through the addition of more clusters, it is not a divergent change. But if the clusters dissolve and form a decentralised, homogeneous network then the change is divergent. A change in network structure refers to the differences observed in its architecture.

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?

[The real distinction between mind and body]

It is clear that the question he promised to answer still remains outstanding: how does it follow, from the fact that he is aware of nothing else belonging to his essence, that nothing else does in fact belong to it? I must confess that I am somewhat slow, but I have been unable to find anywhere in the Second Meditation an answer to this question. As far as I can gather, however, the author does attempt a proof of this claim in the Sixth Meditation, since he takes it to depend on his having clear knowledge of God, which he had not yet arrived at in the Second Meditation. This is how the proof goes:

We must pause a little here, for it seems to me that in these few words lies the crux of the whole difficulty.

First of all, if the major premiss of this syllogism is to be true, it must be taken to apply not to any kind of knowledge of a thing, nor even to clear and distinct knowledge; it must apply solely to knowledge which is adequate.

I will now shut my eyes, stop my ears, and withdraw all my senses. I will eliminate from my thoughts all images of bodily things, or rather, since this is hardly possible, I will regard all such images as vacuous, false and worthless. I will converse with myself and scrutinize myself more deeply; and in this way I will attempt to achieve, little by little, a more intimate knowledge of myself. I am a thing that thinks: that is, a thing that doubts, affirms, denies, understands a few things, is ignorant of many things, is willing, is unwilling, and also which imagines and has sensory perceptions; for as I have noted before, even though the objects of my sensory experience and imagination may have no existence outside me, nonetheless the modes of thinking which I refer to as cases of sensory perception and imagination, in so far as they are simply modes of thinking, do exist within me – of that I am certain.

In this brief list I have gone through everything I truly know, or at least everything I have so far discovered that I know. Now I will cast around more carefully to see whether there may be other things within me which I have not yet noticed. I am certain that I am a thinking thing. Do I not therefore also know what is required for my being certain about anything? In this first item of knowledge there is simply a clear and distinct perception of what I am asserting; this would not be enough to make me certain of the truth of the matter if it could ever turn out that something which I perceived with such clarity and distinctness was false. So I now seem to be able to lay it down as a general rule that whatever I perceive very clearly and distinctly is true.

Yet I previously accepted as wholly certain and evident many things which I afterwards realized were doubtful. What were these? The earth, sky, stars, and everything else that I apprehended with the senses. But what was it about them that I perceived clearly? Just that the ideas, or thoughts, of such things appeared before my mind. Yet even now I am not denying that these ideas occur within me.

[Cogito ergo sum (‘I am thinking, therefore I exist’)]

I see that you conclude that this proposition, I am, I exist, is true whenever it is put forward by you or conceived in your mind. But I do not see that you needed all this apparatus, when on other grounds you were certain, and it was true, that you existed. You could have made the same inference from any one of your other actions, since it is known by the natural light that whatever acts exists. [Fifth Objections: CSM II 180]

When you say that I ‘could have made the same inference from any one of my other actions’ you are far from the truth, since I am not wholly certain of any of my actions, with the sole exception of thought (in using the word ‘certain’ I am referring to metaphysical certainty, which is the sole issue at this point). I may not, for example, make the inference Ί am walking, therefore I exist’, except in so far as the awareness of walking is a thought. The inference is certain only if applied to this awareness, and not to the movement of the body which sometimes – in the case of dreams – is not occurring at all, despite the fact that I seem to myself to be walking. Hence from the fact that I think I am walking I can very well infer the existence of a mind which has this thought, but not the existence of a body that walks. And the same applies in other cases. [Fifth Replies: CSM II 244]

When someone says ‘I am thinking, therefore I am, or I exist’, he does not deduce existence from thought by means of a syllogism, but recognizes it as something self-evident by a simple intuition of the mind. This is clear from the fact that if he were deducing it by means of a syllogism, he would have to have had previous knowledge of the major premiss ‘Everything which thinks is, or exists’; yet in fact he learns it from experiencing in his own case that it is impossible that he should think without existing.

‘I would not urge anyone to read this book except those who are able and willing to meditate seriously with me’, Descartes says to his readers in the Preface (p. 9, below), and he makes it clear that he means the Meditations not to be a treatise, a mere exposition of philosophical reasons and conclusions, but rather an exercise in thinking, presented as an encouragement and a guide to readers who will think philosophically themselves. Its thoughts, correspondingly, are presented as they might be conducted by its author – or rather, as though they were being conducted at the very moment at which you read them. Indeed, the ‘I’ who is having these thoughts may be yourself. Although we are conscious, in reading the Meditations, that they were written by a particular person, René Descartes, and at a particular time, about 1640, the ‘I’ that appears throughout them from the first sentence on does not specifically represent that person: it represents anyone who will step into the position it marks, the position of the thinker who is prepared to reconsider and recast his or her beliefs, as Descartes supposed we might, from the ground up.

This ‘I’ is different, then, from the ‘I’ that occurs in the Replies to the Objections. (Extracts from both of these also appear in this volume; how they came to be written is explained by the translator in his Note on the text, p. xlix.) In the Replies, Descartes speaks straightforwardly for himself, and the ‘I’ represents the author of the Meditations. The ‘I’ in the Meditations themselves represents their narrator or protagonist, whom we may call ‘the thinker’. Of course the author has to take responsibility for the thinker's reflections. He takes responsibility both for the conduct of them and for their outcome, where that includes the beliefs to which we shall have been led if we are persuaded by the arguments, and also the improved states of mind that the author expects us to reach by following his work. But the author is not answerable for every notion entertained by the thinker and for every turn that the reflection takes on the way.