Philosophy of science and medicine X: Aristotle to the early 20th Century

Philip R. Liebson
Chicago, IL


What is natural law? There are certain values in human nature that can be understood through human reason. This implies the use of reason to evaluate binding rules of moral behavior. Inherent in the use of reason, from the Greek philosophers onward, at least in Western Civilization, is the use of logic to assist in the structure of words to describe and evaluate natural law- “logic” or the word. This essay will be discussion of the evolution of logic and the concept of natural law from the Greek period, through the medieval era and so onto current philosophical principles. Although the concept of “natural law” has evolved into the empirical basis of universal laws, the philosophy of logical thought has continued to evolve.

If we are to list what might be considered current natural laws that affect us in everyday life

They might include laws of attraction, vibration, relativity, cause and effect, polarity, rhythm, gestation, and transmutation, among others.

Although the concept of natural law has been associated with common law, natural law is considered separate from law based on human rights. However, the concept of natural law has been used in the development of common law by the use of reason to assess human behavior.

Greek philosophers separated the concept of law and nature in that nature was universal, but law itself varied from place to place based on local customs. For example, according to Plato, who sometimes used the term “natural law”, the orderly universe that is around us consisting of such elements or forms as goodness and beauty. In the medieval period, St. Thomas Aquinas used the concept of natural law to establish reasons for action and to create moral obligations.  The concept of natural law has been used in the establishment of the French Declarations of the Rights of Man and the U.S., Declaration of Independence and Constitution.

The use of logic in establishing concepts of natural law can be seen in early works such as Aristotle’s Organon, composed of his Prior Analytics, Posterior Analytics, and Sophistical Refutations. These include the concepts of induction and deduction in establishing universal concepts. The term “universal” has been attributed to Aristotle as indicating “the whole” as opposed to the particular. Thus “horse” and “human” are universal terms, and a specific object is a particular. Aristotle developed the earliest concepts of formal logic. In the early medieval period in the West, the use of logic was based on some of the earlier works of Aristotle and Boethius’s analysis of Aristotelian logic. Efforts were made to apply logical analysis to theology, influenced by Peter Abelard’s Logica Ingredientibus.

By the fourteenth century in Western Europe, several newer developments in the foundations of logic were formulated, fairly independent of Aristotelian concepts. These included theories of supposition, syncategoremata, and consequences. These theories concern, respectively, the range of suppositions about a statement (does the meaning of a term change in context over time?), the use of terms necessary for logic (such as “if” and “not”), and the effect of a cause (“if…then”).

These theories were propounded by William of Ockham (c 1287-1324), influenced somewhat by Boethius and Aristotle in the structuring of the discussion. The content includes discussion of the relationships of written, spoken and mental language (thought), the differences between abstract and concrete terms, and the relationship of hypothetical propositions to truth (“suppositions”).


The seventeenth century initiated textbook traditions in the growth and development of concepts of logic, either based on Aristotelian principles or as a reaction to these principles. In 1662, Pierre Nicole, a French theologian, published Logic, or the Art of Thinking, an extremely influential work over the next two centuries. It derives partially from Descartes in that propositions are combinations of ideas rather than terms. Thus, verbal propositions may be considered signs of ideas, either as affirmations or negations.  In 1620 Francis Bacon published Novum Organon in which he rejected Aristotelian syllogisms in favor of inductive reasoning based upon empirical observations leading to axioms and propositions. In terms of empirical phenomena one may evaluate every situation in which a phenomenon is found, similar situations in which a phenomenon is not found, and situations in which the phenomenon may vary. This allows an indication of the nature of the particular phenomenon. This concept is in fact in use in clinical medicine and other disciplines in evaluating cause and effect relationships.

In the nineteenth century, we begin to see the influence of what we could proudly term introspection and psychologic insights into the texts of logic in philosophy. John Stuart Mill (1843-A System of Logic) ascribed the foundation of logic to introspection and psychologic elements, a view that would be emphasized by German logicians over the next half-century. Georg Hegel in his Science of Logic (early 19th century) used a transitional approach from the most empty and abstract categories to the absolute, containing and resolving all categories that precede it.  Here he uses his dialectic method to reach a resolution of categories by linking a concept with its contrary premise and transitioning the resulting concept though further linkages and resulting premises (thesis and antithesis) until the rational structure of the “absolute” is reached. Thus, there is no series of valid inferences from one premise to another but a blending of possibly contrary concepts until resolution of the categories. Of course, this later became the basis for Marxist philosophy and is contrary to stepwise valid inferences that are displayed in scientific theorizing.