Medieval philosophy is an outgrowth and continuation of ancient philosophy. Plato, Aristotle, the Stoics, and the Neoplatonists formulated philosophical insights that, in the medieval period and together with revelation, yielded a number of outstanding, well-ordered visions of reality. "Scientifically well ordered" is a predominant characteristic of medieval philosophy and theology, especially in its more mature phases. This is certainly not true of Plato's dialogues taken either severally or as a whole. Though truer of Aristotle, his extant writings still left certain fundamental issues open for intense debate, development, and resolution. Moreover, his First Philosophy, which we now call the Metaphysics (the treatise that comes closest to presenting his fundamental science of reality), is a posthumous compilation of his different insights into first and dependent causes and into the unified character of general reality—rather than, as medieval thinkers would later aspire to achieve, an integrated science of this subject. Nevertheless, Plato and Aristotle, the fathers of the two most influential philosophical currents in the Middle Ages, do adhere consistently to discernible methodologies that greatly informed the fundamental frameworks of medieval outlooks. Choosing between the Platonic and Aristotelian approaches as starting points for a philosophy became, for medievals — as for many even today—a basic decision, one with far-reaching consequences. Though sharing enough to be synthesized by some into one vision, subsequent philosophers were aware of the irreducible fundamental differences of these two perennial approaches. This forced those who combined them to choose either one or the other as a starting point.
Plato's basic insight is that the mind's assessment of sense experience appeals to sources only seen, however obliquely, with the mind's eye. When we judge, for example, one thing to be better than another, we appeal to a standard of goodness. This standard cannot appear to us through the senses. If it did, it would not really be the true standard, for then we would still be able to judge it itself in relation to other things, necessitating a higher norm in accord with an invisible standard of goodness. Though we appeal to goodness as a standard of judgment, we do not understand goodness itself perfectly, and we experience much difficulty when trying to give a scientific account of it. However, forms such as goodness are each understood as one unchanging essence. If goodness were somehow many or were of different types, it would need be judged to be a good thing, and that by which it would be so judged would then be goodness itself. The soul that judges by means of these perfect forms possesses, therefore, some knowledge of an unchanging measure, however imperfect that knowledge may be.
True knowledge, properly speaking, can only be of unchanging things, since they alone can yield unwavering truth and provide a norm for judging changing realities. Of changing things, namely sensible things, we can only have opinion, not true knowledge. Man's access to unchanging realities that transcend the sensible world is evidence, for Plato, of the preexistence of the soul. The soul must have lived in a world of unchanging realities before its birth into its present earthly existence. The access to unchanging realities is not explainable in terms of our present sense experiences, which are of changing things, yet some knowledge of unchanging realities is now present to us. So it can only be present to us as something we remember from our pre-earthly life. These basic insights pervade Plato's dialogues, and they provide keys to the further developments of his thought. We cannot here spell out all the developments that are found in his many dialogues, but we can indicate two general consequences of his developed thought (see Plato in the Middle Ages). First, the sensible world, as a copy of a truer intelligible reality, owes its character and order to an ultimate or first source or cause that produced the orderly world we inhabit out of the desire to give of itself, that is, to share its goodness and wisdom. Secondly, the soul, above all a lover of true reality, thirsts for a return to this ultimate source, which is the ground of life, knowledge, and reality.
The central tenets of Aristotle's philosophy likewise depend on his starting point, which is his account of change. Even in the Metaphysics, dealing with topics to be studied after all others, he begins by addressing change as that which first presents itself as a subject for philosophical questioning. The fact of something new coming into being, the most evident of phenomena, must be explained, not explained away, as Aristotle feels his predecessors had done. Plato's unchanging forms, understood by Aristotle as causes separate from changing things, fail by their very definition as unchanging realities to account for change. The same applies to those philosophers who, like Parmenides and Melissus, posit only one principle of being. These thinkers are caught in the following dilemma: either something comes from being or from nonbeing. If from the former, then it already was, and therefore does not come to be. If from the latter, then nothing ever would come to be. Either way, there is no real change, in the sense of something truly new coming into being. On the other hand, claiming that all reality is in flux or is always changing, as Heraclitus and his followers seem to convey, destroys all intelligibility in nature, as there remains no fixed ground for our judgments. When we would speak of anything, it already has passed away or ceased to be. Learning from the failures of earlier natural philosophers to explain change or how something new can come into reality, Aristotle finally arrived at an account of change that was based on three principles: two contraries and an underlying subject. Every type of change is the actualization of a potency.
This portrait of change is dealt with more fully in our entry on Aris-totelianism. Suffice it to say here that in this account Aristotle discovers the immanent forms governing and dictating the goals of all processes, including the human soul as the form of the body. He also discovers the eternal nature of change, the eternal character of the universe that includes it, and the eternal existence of the ultimate cause of all change and motion, the first Unmoved Mover. This first cause, which is pure actuality, governs all things as the ultimate end that each thing approaches through the limited actualization of its form. As natural forms are immanent, the sensible world is not a copy of higher unchanging forms and does not owe its orderly patterns to a Creator. The Unmoved Mover is not an efficient cause. It is complete in itself and has no relation on its part to other things. However, other things are all related to it. They want either consciously or unconsciously to be complete just as the Prime Mover is complete. They do not want to be the Prime Mover, since they do not have the nature or essence of the Prime Mover. However, they do want to be complete according to their natures. Men, for instance, by having a human form or nature, want to be as fully human as they can be. In this way, but at their own level, they try to imitate the Prime Mover, aiming at becoming complete, but complete as human beings. Their immanent form, the human soul, aims them in that direction.
The immanence of forms is not only the key to Aristotle's philosophy of human activity—indeed, it is the key to the activities of all things, whose forms make them the kind of things they are and leads them to do the things they do. The immanence of forms also means that human knowledge of them is abstractive: the intellect knows these forms when it draws them out of the sensible particulars in which the forms are found. We do not arrive at the knowledge of universal principles through recollection of universal transcendent realities we encountered in some previous life. Finally, as the human soul itself is an immanent form, its goal is the actualization of this form or nature, a nature that is fulfilled chiefly through growth in knowledge and moral virtue. When Aristotle says, "All men by nature desire to know," he is not simply giving a description. He is declaring that it is the very nature of man that he wants to know the things that lead to the highest human happiness. Only in pursuing such objects will he be fulfilled as a human being.
More than Plato and Aristotle, the Neoplatonists, particularly Ploti-nus and Proclus, provide explicit philosophical systems, basically syntheses of Platonic and Aristotelian thought. These syntheses, which served as examples for medieval philosophical and theological systems, essentially subordinated Aristotelianism to Platonism: the sensible reality adequately described by Aristotle depends on the more fundamental reality discerned from Plato's writings. Plato's ultimate source is to be understood as the One from which all things emanate (through necessary stages bridging spiritual and material reality) and to which all things seek to return. In general, medieval thinkers try to move beyond the necessity imbedded in this conception, with its concomitant theses, in their pursuit of an intelligible account of the God of revelation who freely created the world.
While "scientifically well ordered" is the characteristic style of medieval speculation, God-oriented is its central tendency. Understanding the most worthy objects of knowledge—namely, God and his works—is the chief task. The resources for this task are reason and revelation. The scientific character of medieval philosophy and theology largely stems from the conviction of the fundamental compatibility of these two sources. The truth is one. How can two contradictories both be true? Re vealed truth is therefore compatible with rational truth. The truth of reason found in the texts of the philosophical tradition must be gathered and synthesized. Such philosophical syntheses in their turn must themselves be examined and judged in relation to the truth of revelation. This attitude is what generated competing visions, all of which used reason to interpret revelation and revelation to orient reason. The philosophies of Plato, Aristotle, and their followers are viewed by medieval thinkers as great intellectual inheritances, since these philosophers concluded, on the basis of reason, truths about God and the world that were often consonant with and illustrative of truths affirmed by revelation. However, the great Greek thinkers did not say all that could be said about God, nor were they free from erroneous judgments. Some of their conclusions stood in need of revision. Inspired by the teachings of revelation and their conviction of the one divine source of the truths found in creation and in revelation, medieval thinkers drew further intelligibility from studying the philosophical tradition and the world they experienced, and formulated well-ordered versions of this intelligibility. These syntheses are neither classical nor modern, but properly medieval, though dependent on classical sources.
To the extent that the wisdom of the classical philosophical tradition still is relevant today, medieval philosophy and theology continue to have something to offer us. To realize this more fully, medieval thought needs to be studied, understood, and appreciated in terms of its own richness, and not according to how it agrees with our present-day ways of thinking. To the extent that solidly based, well-ordered thought can still be one of the aspirations of our life of reason, medieval philosophy and theology provide some of history's best models. How this desire for a well-thought-out unified view of reality can not be an aspiration today is difficult to see. It challenges many contemporary trends that use reason more for the destruction of argument and reasoned discourse, substituting the celebration of personality, or limiting all worth in terms of immediate practical ends. Such trends toward disorder have always existed. The desire to find the fundamental order of reality, as it presents itself in experience and well-informed tradition, remains the purest aspiration of reason, the core of our being. Furthermore, medieval thinkers, in their quest for God, whose presence they found in the proper ordering of the soul and in the beauty of the world, provided some of the most thorough reflections on the spiritual dimensions of reality—reflections that are still relevant in our own present-day search for the meaning of our human existence. In addition, the fruits of their concern for rigor and clarity provide us with some of the best examples of intellectual analysis.
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