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There are three pivotal terms in Spinoza's system: substance, attribute, and mode. Substance that he also paraphrases as God, or nature naturans is in itself and is conceived through itself and its existence does not depend on the: existence of another thing nor does its conception depend on the conception of another things from which it must ,be formed.
Substance is one, unique, cause of itself, absolute, infinite, simple but constituted of infinite attributes each of which expresses eternal and infinite essence of the substance. From these only two attributes are known: thought and extention.
Extention like thought is an attribute of God. Extention is also
active as thought.
Attribute is that which the intellect perceives as constituting the essense of the substance.




Mode is thing which is in something else.That is in the substance not only its existence depends on the existence of some other thing but its conception too is dependent on the conception of the other thing.
The contents of the universe, the finite constituents of infinite nature are called by Spinoza modes which follow with eternal nessesity from the essense of infinite substance. In the same way that from the nature of triangle follows the fact that the sum of its angles are equal to two right angles. Therefore the system of existence is called the system of modes.
In this paper entitled "Nature as a System of Modes" we shall briefly discuss Spinoza's main views on this subject.