Epilogue

The ‘Epilogue’ concludes that it is possible to trace important elements of Leibniz’s way of thinking back to many different traditions, all of them reshaped and remodelled with the help of conversations with many hundreds of individuals, into a strikingly original outlook. It was in order to explain the actual world as we experience it, and what good and evil we find in it, that Leibniz took us on a journey through possible worlds and the mind of God. This theoretical understanding was for him at the core of an ultimately practical project of scientific advancement for the benefit of humankind.

9. Monads, corporeal substances, and bodies

‘Monads, corporeal substances, and bodies’ explores the relationship between monads and the extended bodies of the physical world. How Leibniz conceives bodies in his mature metaphysics is one of the most discussed issues in recent decades. In particular, specialists debate whether Leibniz’s metaphysical model allows for genuine corporeal substances. Leibniz writes repeatedly about corporeal substances: the question is how these writings should be interpreted. Are corporeal substances quasi-Aristotelian substances, irreducible to monads, and hence the primary substances of a competing metaphysical model? The problem is that Leibniz never provided a Summa of his philosophy or metaphysics so it is not known whether he had a final settled view.

8. Monads

From 1695 Leibniz came to the view that the best way to capture what it is to be a substance is through the concept of ‘monad’. ‘Monad’, Leibniz explained, comes from the Greek monas ‘which signifies unity, or that which is one’. ‘Monads’ outlines Leibniz’s counter-intuitive metaphysical model by explaining his definitions of unity, simplicity, activity, force, perception, and appetite. His view was that simple, immaterial, non-extended, indivisible entities are the condition of the existence of composed, material, extended, divisible entities. The world of extended bodies studied by physics is ultimately intelligible only if we postulate metaphysical entities that must exist in order for those extended bodies to exist.

7. What is ultimately real—unity and activity

‘What is ultimately real—unity and activity’ uncovers Leibniz’s views about what is ultimately real in this actual world of which we have experience. What are the most fundamental, really existing things? Leibniz thinks the most fundamental entities are individual ‘substances’. But what is it to be a ‘substance’? Embracing the traditional insight that a substance must be endowed with intrinsic unity and activity, he devises his own version of this view, pointing at our own mind as the paradigmatic example of what it is to be a substance, namely a being one per se which is the source of its own internal activity.

5. Complete-concept theory, theory of truth, and theory of knowledge

Leibniz maintained that the principle of identity/non-contradiction implies that every true predication must have some foundation in the nature of that thing. Otherwise A would not be A. If everything is connected to everything and all denominations are intrinsic, what does this mean for an individual in a possible world? ‘Complete-concept theory, theory of truth, and theory of knowledge’ considers Leibniz’s thoughts on individual substances, complete concepts, and truths. Leibniz’s complete-concept theory and his theory of truth as inclusion of the predicate in the subject also lead to his theory of knowledge. His views on innatism and ‘minute perceptions’ are also discussed.

3. Encyclopaedia, scientia generalis , and the academies of sciences

The characteristica universalis was intended to provide the key instrument of a scientia generalis leading to the development of a new kind of encyclopaedia of all the sciences. ‘Encyclopaedia, scientia generalis, and the academies of sciences’ describes Leibniz’s plan to undertake the collection and systematic reorganization of all available knowledge into an updated version of Johann Heinrich Alsted’s universal encyclopaedia of all the arts and sciences. The ‘inventive’ or ‘demonstrative’ encyclopaedia could be expounded as a result of the systematic and cross-disciplinary application of relevant principles and methods. Leibniz was aware that this project should be a collaborative enterprise undertaken on a scale that only an enlightened ruler could support.

2. Characteristica universalis , logical calculus, and mathematics

How did Leibniz propose to pursue his all-embracing programme of scientific advancement? What were the core projects that held his wide-ranging intellectual life together? ‘Characteristica universalis, logical calculus, and mathematics’ explains that Leibniz nurtured the dream of developing an alphabet of human thoughts leading to the creation of a characteristica universalis: a universal system of signs designed to eliminate the ambiguity of natural language. This project progressed into the development of a logical calculus. Over and above the provision of a means of universal and unambiguous communication, however, the characteristica universalis was conceived by Leibniz as a powerful tool of scientific discovery and judgement on the model of algebra.

6. The best of all possible worlds and Leibniz’s theodicy

‘The best of all possible worlds and Leibniz’s theodicy’ explains that Leibniz’s claim that the world we live in is ‘the best of all possible worlds’ is deceptively simple, but based on complex logical and metaphysical machinery. It is an a priori claim in that it does not follow from an observation and evaluation of the balance of good and evil in experience to the conclusion that this is the best one can reasonably expect. It follows instead, independently of whatever experience we may have of the quantity and quality of evil mixed with good, from consideration of the attributes of God, whose existence Leibniz regards as a demonstrable truth.

4. Possible worlds and fundamental principles

Leibniz’s commitment to the characteristica universalis and the scientia generalis rested on his conviction that logic is a mirror of the structure of reality. In his view, the principles that govern thought also governed reality. Reality, for Leibniz, meant first and foremost God, the eternal and infinite being encompassing all perfections. It is from Him and His eternal thoughts that the story of the world in which we find ourselves begins. Logic therefore led via metaphysics to philosophical theology. ‘Possible worlds and fundamental principles’ outlines some of Leibniz’s trademark philosophical views including on possible worlds, possible beings, identity, and the principles of non-contradiction and sufficient reason.

1. Who was Leibniz?

Gottfried Wilhelm Leibniz (1646–1716) lived an extraordinarily rich and varied intellectual life in troubled times. Although remembered as a great thinker, he was a man who more than anything else wanted to improve the life of his fellow human beings through the advancement of science, and to establish a stable and just political order in which the divisions amongst the Christian churches could be reconciled. ‘Who was Leibniz?’ considers the scintillating intellectual development of the young Leibniz and then outlines the next forty years of Leibniz’s life, which were characterized by his attempts to stretch the narrow brief of his official duties to further his all-embracing plan of reform.