When we come to Spinoza’s analysis of affects the fundamental distinction is between active and passive ones. This is because the essence of singular things is to be understood in terms of power. Since only existence is what distinguishes one thing from the other, each thing seeks to preserve its own existence (‘Each thing, as far as it can by its own power, strives to preserve in its being’ IIIP6), otherwise it would cease to be what it is. Any singular thing, however, is also linked to an exterior environment, and the more complex it is, the more complex these relations will be. What defines the nature of human beings, is not some ‘natural perfection’, or that they are created in the image of God, (all ideas guilty of the worse kind of anthropomorphism for Spinoza), but the complexity of their bodies and therefore the complexity their relations to other external bodies. These relations can have two basic forms either active or passive: either I determine myself in relation to these external bodies, or they determine me, and the more that I determine myself the more my power increases, and less I determine myself, or the more that I am determined by external causes, the more my power decreases.
The distinction between passive and active affects is understood by Spinoza through two fundamental affects: joy and sadness. We might say that for Spinoza human affective life is made up of three basic affects: desire (conatus – the striving for self-preservation that all singular things have), and then joy and sadness. All the other emotions that Spinoza describes in the Ethics are merely variations of these three basic affects but the most fundamental are joy and sadness. How can we understand this difference between joy and sadness? Spinoza explains it in proposition 11 of Part 3:
The idea of any thing that increases or diminishes, aids or restrains, our body’s power of acting, increases or diminishes, aids or restrains, our mind’s power of thinking.
Whatever increases or diminishes the power of the body to act also increases or diminishes the power of the mind to think. This follows, Spinoza writes in the demonstration, from 11P7 and IIP14. The first is the statement of parallelism – the order and connection of things is identical to the order and connection of ideas – and the second is that the mind contains what the body experiences, and the more complex a body is the more sophisticated these experiences are. In the scholium, Spinoza explains that our minds, because of the complexity of our bodies can go through many changes. These changes, to use Bennett’s expression, are to be thought in terms of ‘up and a down’, as the passage from a great or lesser perfection (Bennett 1984, p.257). What does Spinoza mean by ‘perfection’ in this context? Again we have to remind ourselves that for Spinoza human beings are not a ‘dominion within a dominion’. We are part of the universe of infinite series of causes and effects, about which we cannot have absolute knowledge. The human body is essentially vulnerable to external bodies, because it has so many complex and involved relations to them. To increase my power to act is to increase my power to determine myself and act against these external bodies through the desire of self-preservation, and my power to act is decreased when these external bodies threaten by existence. I can only be destroyed, Spinoza writes, by external causes. Perfection is an affirmation of existence. The more perfect something is the more reality that thing has, and therefore the more power to act it has and thus the more power to think.
It is with respect to this increase and decrease of the power to act that we can understand the two fundamental affects joy and sadness. Joy is the affect by which the mind passes to a greater perfection, and sadness to a lesser one. There are things in the world that make us joyful and there are things in the world that make us sad. This is all that we need to understand passive affects. First of all these affects have to do with the body, but we know from part 2 that the mind is the idea of the body and that the power of the mind to imagine things depends on the existence and relation of the body. Thus joy and sadness, at least for human beings, does not just involves direct relations with our bodies, but also with our imagination, the idea of the bodies we have, and the ideas of how they are changed or modified by external bodies (whether persons or objects). For the most part, because of the very way we do have ideas of our body, these ideas are inadequate (because we do not have an adequate understanding of the relation our body to the other bodies).
As long as the body is affected by an external body, Spinoza writes in the following proposition, the mind will regard that body as present, and as long as the mind imagines that external body as present, then our own bodies will be affected in the same way. This means that if the mind imagines an external body that increases the power of the body to act then the mind’s power of thinking will be increased, and it will feel joy, and if it imagines an external body that decreases the power of the body to act then the mind’s power of thinking will be decreased, and it will feel sadness. Then mind, then, Spinoza states in the corollary of IIIP13, will try to stop imagining those things that restrain the power of that body and its own, and in the scholium this explains the difference between love and hate. One who loves strives to make present the thing he loves, because this is a passage to a greater perfection through the idea of an external cause, joy, and one hates, for the opposite reason, will try to destroy the thing that she hates.
Through imagination we have, therefore, very complex relations to external bodies. It means in IIIP15 that anything can be the accidental cause of joy or sadness, and we can love or hate those things without any cause known to us because they are similar in our imagination to other objects that affect us. Thus, as in IIIP16, by the mere fact that there is a resemblance to one object or another, we can be affected by joy or sadness. Moreover imagination also opens us up to time. We are affected by the same joy or sadness, Spinoza argues, whether we are talking about a past or future external body, or whether we are speaking about a present one. Thus the imagination retains past impressions of encounters which still affect it in the present, and as the same time can project these impressions, both present and past ones into the future. As long as I am affected, Spinoza writes in the demonstration, I will regard the external body as present, even if it doesn’t exist. The image of an external body is the same whether it exists in the past, present, or future; it is there in my mind, and it affects me. We might say that accidental causes of affects are always the mediation of one affect by another affect, either through different affects, or different times. In each case, for Spinoza, the causes of these affects are inadequately understood and thus experiences passively, whether they are sad or joyful.
It is the intersection between affects and affections which determine the specific nature of human emotions. The mind strives to imagine and recollect images that augment the power of the body to act, and to keep before those ideas which exclude the existence of things that diminish my power to act. It is these images that carry associative feelings from the past, which reflect the causal interactions between my body and others that have left their traces within me, such that different bodies with different traces will react differently in the present then I will. My body is all my past interactions which affect my mind carried through into the present and projected into the future.
Our relation to affects is not merely individual but social (and this will be very important in part 4, to show that the self-interest does not contradict friendship and sociability). It is true for Spinoza that each being strives to exists, but the form that this striving takes is determined by the nature of that being. Human beings are social beings. This means that my own well-being is inconceivable without others. I am not first an isolated being which then encounters others; rather, my very individuality is inconceivable without my relations to others that care for me, and I care for them. It is not that the individual pursues his or her own interests against the interests of others but that to be an individual is to be already acted upon and act with others. My existence, as a determinate mode of infinite substance, is already involved with the existence of others. This is why from IIIP21 Spinoza argues that if we imagine the thing that we love affected with joy and sadness, then we too will be affected by joy and sadness and we will love those who affect those we love with joy, and hate those who cause them sadness. We too also feel empathy towards other beings like ourselves (IIIP27). If the nature of an external body is like our body, then if we imagine that body involving an affect, then we too will be affected by that same affect, which explains the feeling of pity that we have for those that suffer. For human being, affects are imitative. We do not only affirm ourselves but also those we love. Those we love are those whose existence gives us joy, and we wish to give them joy, and exclude from existence everything that gives them or us sadness. This is not altruism as an idea but the power of imagination. If we imagine someone like us to be affected by an affect, we can likewise imagine ourselves also so affected and so also be affected. This similarity is not one of common identity but a direct apprehension through bodily awareness. Thus in every bodily experience there is a direct relation to other bodies and this must always be the case for human beings. And this is both the cause of conflict and harmony. Every human emotion, whether positive or negative, is caused by bodily imaginings, and our ideas of good and evil arise out the joy and sorrow of being in our bodies. What is good is not what we judge but what we desire. We judge it good only because we desire it, and not the other way around.
There is no Good and Evil in the moral sense. Rather they are relations between bodies. What is good is what augments my existence; what is bad is what diminishes it. If we think of this in terms of food, Deleuze explains, then what is bad for us is what destroys our bodies (Deleuze 1983, p.34). This is what we mean by poison. What is good is what suits our nature, and what is bad is what doesn’t. If something suits our nature then it increases our power, if it doesn’t, then it decreases it. Thus, as Deleuze writes, the aim of the Ethics is replace transcendent morality with an immanent ethics, which is nothing else than the relation between bodies (Deleuze 1983, p.35). It follows from this that Spinoza does not see any benefit to sadness at all. Sadness does not teach us anything. It only makes us weak, and from this weakness arise feeling of ‘hate, aversion, mockery, fear, despair…, pity, indignation, envy, humility, repentance, abjection, shame, regret, anger, vengeance, cruelty…’(Deleuze 1983, p.39).
Every individual, for Spinoza is a singular essence, which is a degree of power. This degree of power is determined by an ability to be affected. Thus an animal is not defined, Deleuze explains, in Spinoza as a species, but in terms of its power to be affected, by amount of affections that it is capable of (Deleuze 1983, pp.39–43). When it comes to human beings this power of being affected is defined by two types of affections: actions and passions. Actions explain the nature of the individual (what it can do) and passions how it is affected by external bodies. The power to be affected is present as the power to act, when it is ‘filled’ by active affections of the individual, and the power to suffer when it ‘filled’ by passions. For every individual the power to be affected is constant, but the relation between active and passive affections is variable. It is not only important, however, to distinguish between actions and passions, Deleuze adds, but between two kinds of passions. If we encounter an external body which does not suit us, then the power of this body is opposed to the power of ours and as such it acts as a ‘subtraction’ or ‘fixation’. It takes diminishes or subtracts from our power to act, and the passions that correspond to this relation are sad. In the opposite case, if we encounter an external body that suits us, then its power is added to ours, and we are affected by the passion of joy. Now joy, just like sadness must be separated from our power to act, since it is a passion and must therefore have an external cause, but the power to act increases proportionally such that we reach a point where passive joy ‘transmutes’ into active joy. There cannot be, however, any active sadness, because sadness by definition decreases the power to act and thereby, the power to exist, and not being does not seek to preserve its existence. Suicide, for Spinoza, is not a sign of strength but weakness: a more powerful cause outside of me causes me to take my own life, if even I think mistakenly that I am the cause.
All the sad emotions and passions of our lives represent the lowest point of our power, and thus of our existence. Sadness alienates us from ourselves. We are totally at the mercy of feelings that come from the outside, and totality powerless from stopping them. Only joy can help us to act. If we allow ourselves to be affected by those things that bring us joy, then we become more powerful and more active. One issue for Ethics, then, is how can we experience the most joy so that this feeling of joy can be transformed into ‘active free sentiments’ especially since our nature since to make us so vulnerable to sadness and unhappiness (are we not the most miserable creatures on this planet?), since we are constantly affected by external bodies that we do not understand. How then can we affirm ourselves when we are buffeted from negative passions from all sides? This is the question that part 4 will seek to answer.
Bennett, J., 1984. A Study of Spinoza’s Ethics, [Indianapolis, IN]: Hackett Pub. Co.
Deleuze, G., 1983. Spinoza : philosophie pratique, Paris: Éd. de Minuit.
Lloyd, G., 1996. Routledge Philosophy Guidebook to Spinoza and the Ethics, London; New York: Routledge.
Rorty, A.O., 1987. The Two Faces of Spinoza. The Review of Metaphysics, 41(2), pp.299–316.
 This is always relative for Spinoza, since as finite determinate modes, human beings can never totally be separated from external causes. The aim of the Ethics cannot be to rid ourselves of affects, since they belong to our nature, but to understand them better. Whether we do so is itself is not up to us. Self-determination is not free will for Spinoza but the recognition of necessity (Rorty 1987).
 Bennett lays these out, though he is not convinced that Spinoza should treat desire in the same way that he does joy and sadness (Bennett 1984, pp.263–4).
 Geneviève Lloyd gives an excellent explanation of this (Lloyd 1996, pp.77–6).