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of species came to Darwin while riding in his coach and observing the countryside. “I can remember the very spot in the road … when to my joy the solution came to me…. The solution, as I believe, is that the modified offspring … tend to become adapted to many and highly diversified places in the economy of nature” (Barlow, 1958, pp. 120–121).

Hypotheses and other imaginative conjectures are the initial stage of scientific inquiry. It is the imaginative conjecture of what might be true that provides the incentive to seek the truth and a clue as to where we might find it. Hypotheses guide observation and experiment because they suggest what to observe. The empirical work of scientists is guided by hypotheses, whether explicitly formulated or simply in the form of vague conjectures or hunches about what the truth might be. However, imaginative conjecture and empirical observation are mutually interdependent episodes. Observations made to test a hypothesis are often the inspiring source of new conjectures or hypotheses. As described by Jacob, the results of an experiment often inspire the modification of a hypothesis and the design of new experiments to test it.

The starting point of scientific inquiry is the conception of an idea, a process that is, however, not a subject of investigation for logic or epistemology. The complex conscious and unconscious events underlying the creative mind are properly the interest of empirical psychology. The creative process is not unique to scientists. Philosophers and novelists, poets, and painters are also creative; they, too, advance models of experience and also generalize by induction. What distinguishes science from other forms of knowledge is the process by which this knowledge is justified or corroborated, at least provisionally, by observation and experimentation.

THE CRITERION OF DEMARCATION

Testing a hypothesis involves at least 4 different activities (Ayala, 1994). First, the hypothesis must be examined for internal consistency. A hypothesis that is self-contradictory or not logically well formed in some other way should be rejected.

Second, the logical structure of the hypothesis must be examined to ascertain whether it has explanatory value, i.e., whether it makes the observed phenomena intelligible in some sense, whether it provides an understanding of why the phenomena do in fact occur as observed. A hypothesis that is purely tautological should be rejected because it has no explanatory value. A scientific hypothesis identifies the conditions, processes, or mechanisms that account for the phenomena it purports to explain. Thus, hypotheses establish general relationships between certain conditions and their consequences or between certain causes and their effects. For example, the motions of the planets around the Sun



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