Leibniz and DesCartes And Huygens and Wren
Friday, June 22, 2012 8:36:35 PM
Perhaps the most concise summary of Descartes’ general view of the physical universe is found in part III, section 46 of the Principles:
From what has already been said we have established that all the bodies in the universe are composed of one and the same matter, which is divisible into indefinitely many parts, and is in fact divided into a large number of parts which move in different directions and have a sort of circular motion; moreover, the same quantity of motion is always preserved in the universe. (AT VIIIA 100: CSM I 256)
Descartes argues that mind and body are really distinct in two places in the Sixth Meditation. The first argument is that he has a clear and distinct understanding of the mind as a thinking, non-extended thing and of the body as an extended, non-thinking thing. So these respective ideas are clearly and distinctly understood to be opposite from one another and, therefore, each can be understood all by itself without the other. Two points should be mentioned here. First, Descartes’ claim that these perceptions are clear and distinct indicates that the mind cannot help but believe them true, and so they must be true for otherwise God would be a deceiver, which is impossible. So the premises of this argument are firmly rooted in his foundation for absolutely certain knowledge. Second, this indicates further that he knows that God can create mind and body in the way that they are being clearly and distinctly understood. Therefore, the mind can exist without the body and vice versa.
The second version is found later in the Sixth Meditation where Descartes claims to understand the nature of body or extension to be divisible into parts, while the nature of the mind is understood to be “something quite simple and complete” so as not to be composed of parts and is, therefore, indivisible. From this it follows that mind and body cannot have the same nature, for if this were true, then the same thing would be both divisible and not divisible, which is impossible. Hence, mind and body must have two completely different natures in order for each to be able to be understood all by itself without the other. Although Descartes does not make the further inference here to the conclusion that mind and body are two really distinct substances, it nevertheless follows from their respective abilities to be clearly and distinctly understood without each other that God could create one without the other.
Nemo extensio in longum, latum et profundum, substantiae corporea naturam constituit (extension in length, breadth, and thickness constitutes the nature of corporeal substance). (Principles of Philosophy, Book I).
This is Descartes' definition of matter. He goes on to elucidate it in this way: 'Everything else that can be ascribed to body presupposes extension.' The other qualities of matter, then, are less important and he tells us 'though substance is indeed known by some attribute, yet for each substance there is pre-eminently one property which constitutes its nature and essence and to which all the rest are referred'. The pre-eminent property of corporeal substance which constitutes its essence and nature is extension. The essence of matter then is extension, according to Descartes. As he puts it in his physical treatise 'Le Monde' , referring to matter he tells us 'I conceive its extension, or the property it has of occupying space, not at all as an accident, but as its true form and essence.' Extension is the essence of matter then
The Philosophical foment in Leibniz time clearly attracted his interest, and he set out to hel build the new truth in the shape of his religious and philosophical beliefs and convictions. One of his concerns was the decline in faith in Europe, and he attributes this to the arguments and philosophies of the rationalists amongst whom he counted Newton, due to his Phhilosophia Mathematica.
As a young man he came up with a thesis by correcting the error of his forebears and peers. Defending his thesis revealed to him the need to know more empirical evidence, He had and took the opportunity to learn from the best, but again critically. One of his critical readings of Descartes notes revolutionised his own thesis.
From his religious convictions Leibniz believed in 2 realities of different order or rank. The higher ranked spiritual reality laid down principles that governed the material reality. By these principles a thesis or proposition could be judged as in error or in compliance.
That spiritual principles should govern material was advanced as supporting the divinity of god, the existence of god and the nature of god. However, some were not interested in supporting these ideas, per se, and whether it is in contradiction of them or worse in simple disbelief in them , they still maintained a vibrant interest in empirical exploration of these relations in the material world. These skeptical scientists were the ones Leibniz felt impelled to convince, as well as to eradicate error so that god might be more perfectly known.