(I) Background -- the self in ancient and medieval philosophy. Plato -- soul as capacity to grasp both ideas and sensation. Aristotle -- empirical soul as capacity to direct an individual life to its ends, but also a general soul , nous, as the capacity to understand pure thought. In expressing these concepts, both Plato and Aristotle tend towards reifying and thus mythologizing the soul. Neoplatonism takes up the notion of the soul as a thing, and assigns distinct places in its hierarchical order of being for the general and individual soul. Averroism erases true individual subjectivity from this picture by arguing for the unity of thinking; in this view the individual thinks by unifying himself with the absolute intellect. Scholasticism rejects this effacement of the individual subject for reasons both religious -- an individual subject is a requirement for personal salvation -- and methodological -- we experience thought only through individual thinking selves.
Petrarch's assertion of intellectual individuation is essentially aesthetic -- a delight in multiplicity.
For Cusa, intellect can only exist in relation to the sensible. Intellect consists in defining and distinguishing experience. It not the fact of thinking but its distinct content resulting from different concrete circumstances which provides the principle of intellectual individuation.
Ficino's variant of Neoplatonic thought is centered on eros. The traditional Platonic (and also Neoplatonic) conception of eros consists in a striving on the part of the sensible for the ideal -- it is the driving force of all becoming. For Ficino, however, this striving is reciprocated -- God also strives and cares for man and the world. All intelligences in fact take care for the sensible as well as striving for the ideal.
This opens the possibility for true Neoplatonic theodicy -- matter is not pure evil, not the opposite of form, but the necessary concomitant of form in which form is realized. Eros unifies matter and form.
Ficino's doctrine is applied to the philosophy of knowledge by Patrizzi -- knowledge and love both seek to overcome the separation of the ideal and sensible -- knowledge as a stage or aspect of the work of eros.
The doctrine of eros also becomes an explanation and justification of the work of the artist -- unifying form and matter.
Common to these and other recourses to eros by Florentine Platonism is a new awareness of subjective consciousness. This individual consciousness is portrayed, however, as having its basis in a soul which is independent of the body. The revival of Aristotelian psychology by the Paduan school presents, starting with Pompanazzi, a counterpoint to this spiritualism.
Pompanazzi contends that the individuation of consciousness depends on the inseparability of souls from individual bodies. He argues that the soul is a function of the body, namely the function which gives order and direction to the body. In this he does not divide an intellectual soul from an animal soul -- intellect is not separable from life.
(II) Both schools conceived of matter in spirit as substances, and tried to reduce or subordinate one substance to the other. Modern view relates spirit and nature functionally. The models provided by scientific research and a new conception of art both contribute to this shift, because they take thought as a creative act which gives structure to nature which nevertheless remains independent.
Petrarch is an early precursor to this shift -- his poetry recovers nature from the medieval view that it is fundamentally evil -- but this ultimately serves the end of self-contemplation rather than investigation.
A nearer antecedent is the trend toward empirical observation of nature in the Quattrocento and Cinquecento. This is taken up in Renaissance philosophy by Telesio's naive, purely deductive empiricism (which is essentially the same as Francis Bacon's empiricism). But this kind of empiricism does not succeed in providing real order to thinking about nature. Even Telesio's followers -- Pico, Campanella, Giambattista della Porta -- seek order within nature by reference to magical or occult causes. (This tendency is fostered by Renaissance philosophy's conception of knowing a thing as a matter of becoming unified with it, which depends in the end on a commonality of substance.)
151-152: "The theory of nature of the fifteenth and sixteenth centuries laid the foundation for exact description and exact experimentation; but closely connected with this, we find also the attempts at the foundation of an 'empirical magic'. The difference between 'natural' and 'demonic' magic lies in that the latter is based on the acceptance of supernatural forces whereas the former wants to remain completely within the framework of nature and of its empirical uniformity, claiming for itself no method other than inductive observation and the comparison of phenomena. But, this form of 'induction' does not yet recognize any kind of analytical-critical limitations, such as are presupposed and lie at the base of every genuine 'experiment'. Thus, the world of experience here borders on the world of miracles, and both constantly overlap and merge with each other. The whole atmosphere of this 'science' of nature is filled to the brim with miracles."
152: "To conceive of experience itself as a mere aggregate, to define it, with Campanella, as experimentorum multorum coacervatio, means that there can be no analysis of its elements and no evaluation of the role played by each individual element in the systematic construction of 'nature'. Such an analysis and evaluation could only be made after a separation of the basic elements of experience had been achieved elsewhere -- after an 'inner crisis' had taken place in experience itself. This separation of the 'necessary' from the 'accidental', this distinction between that which obeys laws and that which is fantastic and arbitrary, was brought about not by the empiricism and sensualism of the philosophy of nature but by the intellectualism of mathematics."
Leonardo takes two key steps towards a modern conception of knowledge. He accords honor to sciences according to their achievement of certainty rather than their subject matter. And he views experience not just as something given, but something that can be analyzed and given order to by thought, and particularly by mathematics. Still, Leonardo retained a bias towards conceiving order or form in terms of vision. His notebooks are a combination of close observations and visual thought experiments (which Cassirer, following Goethe, calls 'exact fantasies') -- which aim at truth as a perfection of seeing. Artistic vision is not differentiated from mathematical analysis.
The theory of science in the Renaissance is linked to the theory of art by a focus on the problem of form. The conception of form in the new theory of art exemplified by Leonardo was just as decisive as the use of mathematics for the formation of a new science of nature. Leonardo insisted that artistic creation was not an imposing of form on nature, but a discovery of order and form in nature, and this view of form in nature was taken up directly Galileo and Kepler.
Cassirer considers the historical analogy between the change in ancient thought produced by Plato and the emergence of new theory of science in the Renaissance. In both cases, an earlier attempt at a direct, superficial empiricism is overtaken by a turn to the ideal and mathematical. The earlier natural philosophy of the Renaissance understood knowledge as a unification with the object. The new art and science both sought to establish a distance between subject and object, and furthermore to analyze nature itself into particulars.
The Platonic account of sensibility, however, saw its significance only as a prompting to knowledge of pure form. The new art and science give a different valence to the relationship between formal knowledge and experience. They expect theory to be applied to and validated by experience.
Significantly, for Galileo even movement became an object of knowledge.
(III) Movement is also at the core of Aristotelian philosophy of nature. But movement involves fundamental qualitative differences, since location itself has a substantial meaning for Aristotle. Just as bodies have fundamental qualities which make them what they are, so do places, and movement depends on the harmony or disharmony between things and places. Modern physics, on the other hand, thinks of location strictly in terms of their measureable relation to other places.
Cusa is the key figure in introducing a relativistic conception of movement and place. This conception has its roots in his view of knowledge as measurement and his argument that measurement requires the positing of fixed points. Seeing fixed points as posited necessarily excludes the possibility of any absolute place or movement. But it opens the possibility of thinking about rules which govern the relative change in location between things. Moreover, these can be universal rules, applying the same way to all parts of the world, because the world is conceived as having uniformity.
Aristotelian conception of space is just the conception of a boundary between a bodies and what encloses them. But these boundaries are mutual boundaries with other objects within their own spaces (except the external boundary of the world itself). So empty space is meaningless in Aristotelian terms. The totality of space is an aggregate, not a systematic condition of individual spaces.
The first step towards a systematic conception of space was to look at space as homogeneous. This is the principle which was grasped by Cusa, but only found its realization with Galileo. For Galileo, this homogeneity is a consequence of understanding space geometrically -- looking at nature as a mathematical order rather than as a collection of substances. In fact, there is a reversal of the Aristotelian dictum that activity follows being. Since our knowledge of motion has a perfectly general, mathematical form, which applies the same way to all physical phenomena, all matter must have the same substance.
Not only did mathematics and geometry shape a new view of motion, but motion reciprocally shapes our understanding of mathematics and geometry. Particularly notable is Kepler's analysis of geometrical solids as a product of the motion of curves. Furthermore, the analytic geometry of Descartes and Fermat, with the use of a system of coordinates whose center is strictly conventional, depends upon the prior overcoming of the Aristotelian conception of space.
Parallel to this, we have Bruno's conception of an infinite, homogeneous world. He arrives at not through physics, however, but through his views of the incontainability of human feeling and the human intellect.