Some people think that philosophical ideas are abstract and irrelevant. Some are. Nevertheless, ideas shape history and culture. Some ideas have been so profoundly influential that eras (particularly in Western civilization) can be classified by them.
All historians recognize the Middle Ages as an era of fascinating diversity, yet it is easily classified (and thus recognized) by certain unifying ideas. Likewise the Renaissance and the Enlightenment! No one should suppose that these eras had sharp chronological limits, as if they began or ended on certain days, but common ideas gradually surfaced. Often these ideas appear first in the minds of leading writers (scientists, philosophers, and theologians). Through the philosophical elite, these ideas spread in the universities (or, earlier, through the monasteries), and then through the arts to the general culture. These ideas and their collective influence form the intellectual models (the worldviews) by which individual facts and events in past centuries are interpreted.
Whereas the intellectual life of Medieval Europe was dominated by Platonic philosophy Plato (c.427-c.347 b.c.), one of the greatest of the ancient Greek philosophers, taught that a spiritual world of universal ideas existed. These ideas were the original forms on which all physical reality was modeled and by which physical reality was shaped. Ultimate reality was exclusively rational and thus could be known by the rational human mind even apart from sensory experiences. Medieval Christianity was not strictly Platonic (since Plato taught that the universal ideas were abstract, impersonal, and autonomous), but it was generally Platonic in style. Medieval theologians held that universal ideas existed, but they located them exclusively in the mind of a personal God. Nevertheless, the emphasis was on a separation between spiritual reality above and physical reality here below. This kind of dualism often led to a depreciation of the physical and an exaltation of the rational (the spiritual). Monastic orders illustrate this tendency by withdrawing from the world in order to be more "spiritual." The lifestyle of a stereotypical monk was one of mystical asceticism or otherworldliness. Medieval art often reflects this dualistic worldview. An introduction to Plato may be found in W. K. C. Guthrie, A History of Greek Philosophy, Vol. 4 (Cambridge: University Press, 1975), and John Niemeyer Findlay, Plato and Platonism (New York: Times Books, 1978). and by belief in God as interpreted by the Roman Catholic Church, the intellectual life of the Renaissance was less abstract and more humanistic. It reemphasized classical Aristotelian forms and ideas. Aristotle (384-322 b.c.), Plato's most famous student, was at one time a tutor for Alexander the Great. Aristotle was heavily influenced by Plato's rationalism, but he ultimately rejected dualism in favor of a materialistic monism that found truth and meaning in particular individual things. Such emphases eventually led to modern, empirical, scientific ways of thinking, but Aristotle's methodology contained many assumptions that depended heavily on common sense or naive observation. These assumptions in some cases prevented scientific progress for many years. For example, Aristotle taught that the natural state of a thing was to be at rest (motionless). His reason for holding this belief was that the earth was the motionless center of the universe (sense perception convinced him of that), and without a causal "mover" nothing would move. Thomas Aquinas took this "accepted truth" as one of his "five ways" to know that God exists. For many years the apparent motion of the heavens was accepted as a solid proof of God's existence. Who else could move all the stars together with such perfect regularity? This common-sense notion about motion was so obvious that it was not until Galileo and Newton that the modern, more dynamic picture of the universe began to emerge. The modern view has a totally different view of motion. It seems as if the natural state of things is to be in constant motion, and the old "first mover" argument has lost its persuasiveness. For the modern mind there is no longer an absolute, no longer a fixed point; the regular motion of the heavens seemingly is an illusion; the need for a personal mover is no longer obvious. This does not mean that all forms of cosmological reasoning are invalid, but the long-accepted version based on Aristotelian views of motion now seems to have been based on a false premise. For an introduction to Aristotle, see John B. Morrall, Aristotle (London: George Allen & Unwin, 1977), and W. D. Ross, Aristotle (New York: Barnes & Noble, 1964). The eighteenth-century Enlightenment was characterized by a decisive shift toward a more secularized form of theology, with the emphasis in theological literature turning toward ethics and religious experience. This was in some ways a reaction to the rapid developments in science that seemed to challenge the theological systems that had so closely aligned themselves with the older Aristotelian scientific assumptions. The influence of Kant and Schleiermacher can be seen in the shift away from accepting the objective teaching of Scripture as being the very Word of God toward a more subjective theology of personal experience and personal opinion.
In the nineteenth century the Enlightenment's emphasis on morality and religious feelings continued and grew, but to this was added a sense of natural historical development and inevitable progress. Every area of life seemed to be affected by the growing secularism of the age. Individual freedom became a high priority (unless someone exercised their freedom in a way that violated another's inalienable right to freedom). But this new, secular freedom ultimately refused to submit even to God, and thus it destroyed the only possible basis for guaranteeing rights and values and freedom.
Nineteenth-century concepts can be seen as forming the axioms and assumptions of "recent modern" man and, in fact, are the keys for unlocking the modern mind. With many new discoveries, many previous scientific theories have had to be modified, but nineteenth-century philosophical ideas still make up much of the distinctive worldview of the so-called modern and postmodern eras. Some believe and proclaim the ideas of evolutionary progress and anti-supernaturalism; others reject and/or criticize those ideas; still others suppose that some mixture of old and new ideas is the correct perspective. Nevertheless, the nineteenth-century secularization of science and history sets the agenda and the pattern for modern thought.
The new features of the modern worldview (natural historical development and inevitable progress) are not necessarily two absolutely distinct ideas. They are usually seen more as a blend, and it is precisely this blend that lies behind modern secular thought. In order to see the impact this blend of ideas has made, it will be helpful to contrast the modern secular and naturalistic worldview that had arisen by the late twentieth century with the idea blend (the worldview) which (in the West, at least) has been secularism's primary rival. This long-standing alternative includes the following ideas: (1) stability in nature, (2) spiritual warfare, and (3) historical change initiated by divine intervention.
This latter set of ideas more or less characterized Christian civilization prior to the nineteenth century, and it has maintained a strong following among Christian philosophers throughout the last two centuries (nineteenth and twentieth). For example, the idea of stability in nature grew out of the biblical teaching about creation. God made everything, saw that it was good, and finished his work of creation (the origination of new kinds of things) on the sixth day (cf. Gen. 1). Animals and plants were thereafter to reproduce "after their kind." This did not mean that variation and adaptation could not occur within the established limits of the biblical "kind," but it did mean that nature was understood as being basically stable. There was order and predictable regularity. This notion, in fact, was an essential element in the worldview that actually nurtured the birth of modern science.
Early modern science (1500-1750) came into being only partially because of new inventions such as the telescope. These instruments were important, but of at least equal importance were the philosophical ideas that supported the discovery of objective truth. Aristotle correctly moved away from a strict rationalism, such as might have been supported by Plato, and emphasized the unity of, for example, math, physics, and biology. Aristotle, however, never exceeded the limits of his own perceptions.
Aristotle believed in the perfection and the unchangeableness of the heavens. That is how they appeared to him. The medieval science that grew out of this Aristotelian notion concluded that the pure fire of the stars was either attached to a revolving, celestial sphere or that the stars were windows by which the pure fire showed through from the glorious realm beyond the pure crystal dome of the night sky. The heavenly perfection of the sun, and of the moon and of each known planet, was also affirmed, each one being given its own revolving sphere of pure transparent crystal.
Aristotle taught that an object's natural state was to be at rest. Thus, motion proved the existence of a "mover," and for Aquinas, though not for Aristotle, the unmoved mover of all things was the biblical God. At this point Aristotle's physics and Aquinas' apologetic assumed the earth to be an unmoving fixed point in the universe; in fact, the earth was the center point of all the universal circles. Thus the rational significance of the earth was without parallel.
Aristotle's medieval followers denied (before and without looking) the possibility of a blemished sun (sun spots), and they could offer no natural explanation for a comet (How did it get through the crystal spheres without breaking them?) or for a nova (stars were supposedly in a state of static perfection). The discovery of such phenomena in Galileo's day threatened Aristotle's science and church traditions, though not the Bible. Alchemy and other medieval "science projects" were also based on incorrect ancient Greek notions about the elemental makeup of the world.