Spinoza’s Ethica ordine geometrico demonstrata (Ethics demonstrated in geometrical order) is based on a deductive method derived from Euclidean geometry. Spinoza maintains that the validity of ethical ideas can be demonstrated by mathematical argument or proof. Spinoza asserts that ethics can be based on a geometric model in which axioms and propositions follow each other with logical necessity. This reflects the view that ethical truth has the same logical necessity as mathematical truth. Spinoza sees ethics as a rational system corresponding to the rational nature of the universe.

The Ethics is divided into five parts: Part I. "Of God;" Part II. "Of the Nature and Origin of the Mind;" Part III. "Of the Origin and Nature of the Emotions;" Part IV. "Of Human Bondage, or Of the Strength of the Emotions;" Part V. "Of the Power of the Intellect, or Of Human Liberty."

Each of the five parts of the Ethics consists of several definitions and axioms, followed by a series of propositions and corollaries.

The propositions of Part III are followed by forty-eight definitions of the emotions, including desire, pleasure, pain, love, hatred, hope, fear, despair, joy, disappointment, humility, pride, anger, shame, cruelty, benevolence, etc.

Spinoza begins by describing what can be known about God. God is infinite being, according to Spinoza. God is infinite substance, consisting of infinite attributes, each of which expresses God’s eternal and infinite essence (I, Prop. XI).¹

God necessarily exists, argues Spinoza, because God’s essence is existence. God’s essence is perfect, and therefore God's perfection implies that God must exist. God’s essence and existence are the same (I, Prop. XX). Each attribute which expresses God’s essence also expresses God’s existence.

According to Spinoza, infinite substance is indivisible (I, Prop. XIII). If infinite substance were divisible, it could either be divided into two finite parts, which is impossible, or it could be divided into two equally infinite parts, which is also impossible. Thus, there is only one infinite substance.

Since God is infinite substance, Spinoza argues, no attribute which expresses the essence of substance can be denied of God (I, Prop. XIV). Every being has its being in God. Nothing can come into being or exist without God.

According to Spinoza, the will and the intellect are modes of thought. The will is the same as the intellect. In God, intellect is actual and not potential, because in God intellect is fully actualized. This means that things must necessarily occur in the manner in which they occur, because the intellect or will of God is fully actualized.

For Spinoza, God is the necessary cause of all things. All things by nature proceed from necessity. All things are predetermined by God, and for anything that exists, some effect must follow.

Spinoza argues that thought is one of the attributes of God (II, Prop. I). God can think an infinite number of things in an infinite number of ways. God’s infinite intellect comprehends all of God’s attributes.

According to Spinoza, God is the essence of substance. Thought and extension are attributes of God. Thus, God is the essence of thinking substance (i.e. mind) and of extended substance (i.e. body).

Substance is defined by Spinoza as a mode of being which implies necessary existence. God is infinite substance, and outside of God no other substance is possible. Thus, Spinoza’s philosophy is pantheistic, in that it claims that God is present in all things.

Spinoza argues that the human mind is a part of the infinite intellect of God (II, Prop. XI, Corollary). All ideas are present in the intellect of God. Ideas are true and adequate insofar as they refer to God. Ideas that logically follow from adequate ideas are also adequate. Ideas are false and inadequate insofar as they do not express the essence of God.

According to Spinoza, an idea is adequate and perfect insofar as it represents knowledge of the eternal and infinite essence of God. Spinoza says that, since the idea of anything actually existing must come from God, the human mind is capable of knowing God (II, Prop. XLV).

For Spinoza, the will cannot be separated from the intellect. There is no such thing as free will, because the human mind is determined in its willing by a cause other than itself. God’s will, which has no cause other than itself, reveals itself by necessity rather than by freedom. Thus, Spinoza explains that the will can only be a necessary cause of action, and not a free cause of action (I, Prop. XXXII).

Spinoza also argues that from any idea, an effect must necessarily follow. Insofar as an idea adequately refers to God, its effect is caused immediately by God. Insofar as an idea inadequately refers to God, its effect has intermediary causes and is not caused immediately by God.

Spinoza explains that the human mind may have both adequate and inadequate ideas. The mind is active insofar as it has adequate ideas, and is passive insofar as it has inadequate ideas. The mind may have more or less adequate ideas, according to whether it is more or less subject to reason. The mind may have more or less inadequate ideas, according to whether it is more or less subject to emotion.

According to Spinoza there are three primary emotions: desire, pleasure, and pain. All emotions arise from desire, pleasure, or pain. Desire may arise from either pleasure or pain. Pleasure may be produced by a transition from a lesser to a greater state of perfection. Pain may be produced by a transition from a greater to a lesser state of perfection.

For Spinoza, perfection is the same as reality II, Def. VI). The more perfect a thing is, the more real it is. Inasmuch as God is absolutely perfect, God is also absolutely real. God is infinitely perfect and infinitely real.

Spinoza claims that the more perfect a thing is, the more active and less passive it is. The more active a thing is, the more it becomes perfect (IV, Prop. XL). Perfection and imperfection are modes of thought.² The mind is most perfect when it knows God.

Spinoza argues that knowledge of good and evil arises from the awareness of what causes pleasure and pain. The greatest good of the mind, and its greatest virtue, is to know God (IV, Prop. XXVIII). To act with virtue is to act according to reason (IV, Prop. XXXVI). If we act according to reason, then we desire only what is good. If we act according to reason, then we try to promote what is good not only for ourselves but for others. Freedom is the ability to act according to reason. Freedom is not the ability to make free, undetermined choices. Freedom is the ability to act rationally and to control the emotions. Servitude is the inability to act rationally or to control the emotions.

Spinoza admits that all emotions may not necessarily conflict with reason. Emotions which agree with reason may cause pleasure, while emotions which do not agree with reason may cause pain. Inability to control the emotions may cause pain.

According to Spinoza, pain is the knowledge of evil. Pain arises from inadequate ideas, i.e. ideas which do not adequately express the essence of God. Knowledge of evil is thus inadequate knowledge (IV, Prop. XIV). Pleasure is knowledge of what is good. Pleasure arises from adequate ideas, i.e. ideas which adequately express the essence of God. Knowledge of good is thus adequate knowledge.

Spinoza argues that to live according to reason is to live freely, and is not to live in servitude to the emotions. If we act according to reason, then we are guided by love and good-will and not by fear or hatred.

Spinoza maintains that reason can control the emotions. Reason is virtue, and virtue is love toward God. The more we love God, the more we are able to control our emotions (V, Prop. XLII, Proof). The better we can control our emotions, the better we can understand God.

For Spinoza, the more active the mind is, the more adequately it knows God. The more passive the mind is, the less adequately it knows God. The more active the mind is, the more it is able to avoid emotions which are evil. The more passive the mind is, the more it accepts emotions which are evil.

The question arises as to whether Spinoza’s philosophy is able to reconcile the existence of good with the existence of evil, or the existence of truth with the existence of falsehood. If God is infinite substance, then how can any kind of evil or falsehood occur? If God is perfect, then how can God allow the existence of evil or suffering? Spinoza’s answer is that evil is a lack of good and that falsehood is a lack of truth. Error and falsehood arise from inadequate knowledge of God. Knowledge of evil arises from inadequate ideas, i.e. ideas that do not adequately refer to God. Knowledge of good arises from adequate ideas, i.e. ideas that adequately refer to God.

Spinoza argues that all ideas are found in God, but that ideas are true only insofar as they adequately refer to God. Truth is adequate knowledge, but falsehood is inadequate knowledge.

Spinoza, Benedict. "Ethic," in Spinoza: Selections. Edited by John Wild. New York: Charles Scribner's Sons, 1930.