Introduction

Nowadays, philosophy and science are two distinct domains, separated bydividing lines that were nonexistent in the past. We often associate philosophy with the examination of unanswerable questions, whereas the core activity of science seems to be the collecting of empirical data and the creation of explanatory mathematical models. In antiquity and in the Middle Ages, however, philosophy and science were one discipline with one shared history.

Medieval natural philosophy did not originate out of nothing; it did not stand on its own shoulders but on those of ancient philosophy. The famous British philosopher Bernard Williams once remarked that ‘‘the legacy of Greece to western philosophy is western philosophy.’’ Before the publication of Newton’s Principia mathematica philosophiae naturalis (1689), Aristotle’s Physics was the most widely read and influential book of natural philosophy. How could Aristotle become such an important authority? The answer to this question is linked to the site of Philosophy during the Middle Ages. After 1200, philosophical and scientific culture primarily flourished at the universities, instead of, for instance, in laboratories or learned societies, cathedral schools, monasteries, or courts. At all universities in medieval Europe, Aristotle’s works came to be compulsory reading for all students. The works of Plato or of other Greek thinkers were hardly known. This historical circumstance shaped medieval (natural) philosophy in a unique way (see the entries on Aristotelianism, in the Greek, Latin, Syriac, Arabic and Hebrew Traditions and Universities and Philosophy in this volume).

In medieval universities, the curriculum of the Faculty of Arts included the seven liberal arts (grammar, rhetoric, logic, arithmetic, geometry, music, and astronomy) and what were called the three philosophies: natural philosophy, moral philosophy (or ethics), and first philosophy (or metaphysics). Aside from astronomy, then, most of the disciplines that were later called ‘‘science’’ fell under the heading of ‘‘natural philosophy” (philosophia naturalis). Other terms that designate the domain of natural philosophy are natural science (scientia naturalis), physics (physica), and, in the post-medieval period, physiology (physiologia).

In addition, medieval scholars were familiar with the term ‘‘science’’ (scientia). It was applied, however, in different ways than we are used to today. In the Middle Ages, the term ‘‘science’’ referred to the mental condition of possessing certain knowledge of something. It was a type of knowledge that was produced by a logical demonstration. In this respect, ‘‘science’’ distinguishes itself from ‘‘opinion’’ or ‘‘view’’ in that the latter are not based on any particular method and are not universally valid and certain. In a derivative sense, ‘‘science’’ can also refer to a discipline in the Middle Ages, a discipline with its own domain of inquiry, principles, and methodology. In this sense, ‘‘science’’ is a collection of propositions about a particular topic, organized in a coherent set of arguments and proofs. Thus, ‘‘physics’’ is a science, but so are metaphysics, medicine, and theology. Overall, scientia, the medieval term for science, was not exclusively reserved for physics, but was applied to any field that contained certain and valid statements (see the entry on Posterior Analytics, Commentaries on Aristotle’s in this volume).

The basic content of philosophy was constituted in medieval universities by the works of Aristotle, known as ‘‘the Philosopher,’’ often accompanied by the commentaries of Averroes, known as ‘‘the Commentator.’’ To fulfill their requirements in natural philosophy, selections were made of Aristotle’s works in natural philosophy. Natural philosophers of the Middle Ages and the Renaissance believed that Aristotle had raised and discussed crucial questions about the natural world and had explained important definitions, general principles, and concepts of physical science. In addition to the Physics, Aristotle had provided this explanation in other ‘‘natural books’’ (libri naturales), such as On the Heavens (De caelo), On the Soul (De anima), On Generation and Corruption (De generatione et corruptione), “Meteorology” (Meteorologica), and The Short Natural Treatises (Parva naturalia). These books were arranged around the Physics as treatises that discussed particular aspects of natural objects. In sum, the medieval and Renaissance scholars found their natural philosophy in the books of Aristotle rather than in the Book of Nature, written in the language of mathematics, as Galileo expressed two centuries later in a very powerful metaphor (see the entries on De caelo, Commentaries on Aristotle’s; De generatione et corruptione, Commentaries on Aristotle’s, and Parva naturalia, Commentaries on Aristotle’s in this volume).

Aristotle as well as the medieval and Renaissance scholars who followed in his footsteps, were utterly convinced of the intelligibility of nature. Nature possesses an order that is accessible to the human mind, an order that initially discloses itself in the way we speak of nature. Investigation of the natural world begins with phenomena (phainomena) and it moves from ‘‘that what is better known to us’’ to ‘‘that what is more knowable by nature,’’ that is, the ‘‘objective’’ principles and causes that are concealed and intrinsic to the phenomena (Aristotle, Physica, 184a17-22 and Metaphysica, 1029b3-12). Aristotle speaks about ‘‘phenomena’’ in a much broader sense than we are used to. For Aristotle, ‘‘empirical data’’ not only refer to the observable facts themselves, but also apply to common opinion or to scholarly opinion about these facts. It is Aristotle’s traditional method to investigate how, for instance, one speaks of a specific topic. He reflects on commonly held views, signals all kinds of problems, and subsequently offers us a more profound analysis of a ‘‘phenomenon.’’

One of the essential research themes in Aristotle’s ‘‘natural books’’ is the phenomenon of change. What is most remarkable about the natural world is that it is susceptible to all kinds of change. Natural objects originate and perish; they are altered; they move (they change location); and they grow. From this perspective, natural philosophy includes the study of celestial bodies, of meteorological phenomena, and of important concepts that are fundamentally intertwined with change, such as ‘‘place,’’ ‘‘space,’’ and ‘‘time’’ and related notions such as ‘‘continuity’’ and ‘‘infinity’’ (see the entry on Atomism in this volume). But it also includes the study of material objects, which have the characteristics of living beings, such as human beings and animals (see the entries on Philosophical Psychology and De anima, Commentaries on Aristotle’s in this volume). For the first time in the history of western thought, a systematic attempt was made to give a conceptual analysis of change and motion, including their temporal and spatial aspects.