Selection from – Ethics – Part I. Of Deus sive Natura (Page 2)
Spinoza's Words: (every cause has an effect)
After the definitions we find axioms (self evident truths) and propositions just as we would find in a geometry textbook..
Axiom III. From a given definite cause an effect necessarily follows; and, on the other hand, if no definite cause be granted, it is impossible that an effect can follow.
Prop. V. There cannot exist in the universe two or more substances having the same nature or attribute.
Prop. VII. Existence belongs to the nature of substance.
Comment:
In Axiom III Spinoza is saying what science today is based upon and takes for granted – that the universe is a place of strict causality. A specific cause produces a certain effect. Although the Axiom seems to be common sense there where many exceptions made by religion of the time. Spinoza also adds to the concept of substance; that there is only one and existence is part of its nature.
Further propositions and proofs make up Book I of the Ethics. They continue on to Prop. XXXVI. Through the proofs using his definitions and logical reasoning Spinoza creates the vision that there is only one substance (the underpinning of the world) and that it exists eternally and is infinite.