The present collection of writings includes all the most critical works of Spinoza, including the Theologico-Political Treatise, the Political Treatise, the Ethics, "On the Improvement of the Understanding", and a collection of Spinoza's Correspondence. It was originally published as two volumes in 1884, and is here reformatted into a single volume. From the Introduction: "Spinoza conceived as a vast unity all existence actual and possible; indeed, between actual and possible he recognizes no distinction, for, if a thing does not exist, there must be some cause which prevents its existing, or in other words renders it impossible. This unity he terms indifferently Substance or God, and the first part of the Ethics is devoted to expounding its nature. Being the sum of existence, it is necessarily infinite (for there is nothing external to itself to make it finite), and it can be the cause of an infinite number of results. It must necessarily operate in absolute freedom, for there is nothing by which it can be controlled; but none the less necessarily it must operate in accordance with eternal and immutable laws, fulfilling the perfection of its own nature."