Descartes Mechanical Philosophy and Leibniz reaction to it. It has 7 sources.
Substance and form
There must be something out of which change takes place." Aristotle thinks that this "out of which" is what we call matter. For Aristotle everything is composed of form and matter. Consider the example of a statue of a doll made of lump of clay, the clay is what Aristotle calls the matter and the shape of doll that it has is called its form. The result is a compound object made of matter and form, the statue of a doll. Still Form and matter are not sufficient to explain change; the statue was first made of clay, which was not first a statue. The contrast between the opposite is not between the statue and the clay [Aristotle, The Physics, 2003]. The contrast is between the non-statues, the lump of clay and the statue. In order for something to change, it must change from not having a particular form into having a particular form. Aristotle concludes that "there are three principles, the underlying substance, the form which is imposed on it and the absence of that form which the substance possessed at the beginning of the process."
In the study of material constitution "there is a great divide." The following example will help understand the different position in the constitution of material: "Tom combined rare soils to create a large lump of clay he called it 'Clayton'. John found the clay on the workbench and shaped it into a beautiful statue of a doll. He named the statue 'Angel' and set it on the mantle." Because the clay statues sell so poorly John decided to replace the clay by lead. John will take a piece of clay from the statue, replace it by lead of same size, till the whole clay statue is replaced by lead, and finally throwing the clay in the garbage. Those who think that material objects can occupy the same place at the same time are called pluralists and those who think that spatial coincidence is impossible are called monists. The pluralists maintain that the lump of clay sat on the workbench last night but the statue did not. The statue could not survive the flattening, but the clay could. According to the Leibniz's law we conclude that the statue and lump of clay are not identical [Moyer 2000].
Philosophy of G.W. Leibniz and Descartes
Descartes another philosopher on the other hand expounded a philosophy which was mechanical in nature. Descartes as we know is a rationalist and explains the existence of the world not from the testimony of the experience but from pure intellect level. According to Descartes we have experience of the world from the innate ideas of the "res extensa.." Descartes held that we have clear and distinct ideas; the clear ideas present one quality and extension and it is distinct from the "res congitans." [Moyer 2000]. This distinct idea granted the reality and of God and thus cannot be wrong. Hence the world exists and the fundamental attribute of the world is the extension. Descartes said that weight, motion, dimension, position and figure are modes of intellect. Hence these innate ideas of qualities and extension are real and objective [Moyer 2000]. The Cartesian world contains the fundamental attribute of extension and it is characterized by this primary attribute and which is infinite: "God is responsible for the force and movement in the world and which are determined by the principle of absolute causality." No teleology governs the world, but a mechanical determination (matter and the mathematical laws of motion) which is responsible for the continuation of phenomena in the physical world in the "res extensa." [The Radical Academy, 2003]. For Descartes the world is a machine, including the inorganic world, the plants and animals and even man. The extension is the essence of the body as we are all including this world machines governed by the laws of causality and motion [Kemerling, 2002].
The entire Cartesian philosophy rests upon a metaphysical dualism between spirit and matter or mind and body. These two realities are irreducible. There is a thinking world and an extended world, just as thought and action are essential to thinking world, similarly mechanical determinism and passivity are essential to the "res extensa." [The Radical Academy, 2003].The interaction between the two substances is impossible. Descartes attached the thought to the thinking substance and argued that the soul's essence is thought. In Cartesian corporeal world matter does not possess any qualities, but only quantity which acts mechanically and fatally [The Radical Academy, 2003].
Leibniz criticized this dualism and the Cartesian mechanism. He believed in the Aristotelian concept of the form and matter, which maintained that form, is drawn out of potency. Leibniz brought his famous theory of monad "a spiritual substance which was not passive and were granted force which spontaneously and according to a law pre-established by God" [The Radical Academy, 2003]. The monad is evolved from a process which is a bit obscure but it gradually reaches the state of representation. Leibniz first of all rejected Descartes concept of extension as the essence of body, Descartes also maintained that all other properties such as, and figure, size, motion and rest are modes of extension. Leibniz on the contrary rejected that idea and said that extension is always extension of something. Leibniz says that an extension is always a repetition, a few extra hours to write the paper, or another few steps on the ladder. Thus when we say that a body is extended it means that it has repeated through its length, width and depth. Descartes had no answer to this question because for Descartes for him an extension of the body is its essence [Burnham, 2001].
In addition in the Cartesian concept the properties of the bodies are principally geometrical if the extension is the essence of bodies. The only way a body can be changed is in size, shape, motion, rest. Descartes believed that change is purely passive and the motion is contagious; it is transferred from one body to another [The Radical Academy, 2003]. The only active substance is the mind which has the power of will while God is the prime mover who has set the universe in motion. Human beings are subject to the laws and have limited control over the universe and over their own bodies. For Leibniz there exists an active element in the corporeal world and that changes occur not mechanically but the things brought about change themselves [The Radical Academy, 2003]. Leibniz held that there is an active component called force in the material things and the laws of nature have to be understood dynamically, as governing the force of acting and resistance. According to Leibniz it is these forces which are extended, he argued that the concept of extension presupposes the substance of body which contains the power of resistance and acting and which is found in every material things and corporeal mass [Scott, 1998].
Rejection of the concept
Thus we have a better concept of the way physical changes takes place, a body is endowed with force a source of activity of potential change within itself, but the body changes according to its own way. For example "when a rubber ball changes its shape when it hits the wall, it happens so due to the internal redistribution of its forces. It bounces off the wall because of its elasticity in springing back to its original shape; it pushes itself off the wall in the reverse direction." According to Leibniz the ability to act is an essential characteristic of a substance and this significant fact is missing in the Cartesian treatment of the extended substance and according to Leibniz it was because of an over-reaction by Descartes to the medieval distortion of the concept of the substantial form. Asserting that appeal to a form can be an empty and meaningless one can still make a proper use of it in metaphysics. The form Leibniz held is what provides the unity of substance which is the only true being. Leibniz argued that a mixture or aggregation is certainly not a unity and it is clearly not a substance. A machine too cannot be categorized as a substantial unity as its parts are combined together externally, similar to that of an army. On the other hand organisms are genuine and are the manifestations of true unity and can be called a substance [Burnham, 2001].
To conclude, there is one difficulty in understanding this concept of "substance and which lies in Leibniz description of the rehabilitated notion of a substantial form." Leibniz responded to the objection that our body and soul are two distinct substances and that one is not the substantial form of another. Leibniz first maintained that the body is not a substance at all, but an aggregated being. Later on he borrowed the Church doctrine which maintains that the soul is…