People refer to a trial solution to a problem as a hypothesis — often called an "educated guess"[5] — because it provides a suggested solution based on the evidence. Experimenters may test and reject several hypotheses before solving the problem.
According to Schick and Vaughn,[6] researchers weighing up alternative hypotheses may take into consideration:
• Simplicity (as in the application of "Occam's razor", discouraging the postulation of excessive numbers of entities)
• Scope – the apparent application of the hypothesis to multiple cases of phenomena
• Fruitfulness – the prospect that a hypothesis may explain further phenomena in the future
• Conservatism – the degree of "fit" with existing recognized knowledge-systems.
[edit] Evaluating hypotheses
Karl Popper's formulation of hypothetico-deductive method, which he called the method of "conjectures and refutations", demands falsifiable hypotheses, framed in such a manner that the scientific community can prove them false (usually by observation). According to this view, a hypothesis cannot be "confirmed", because there is always the possibility that a future
experiment will show that it is false. Hence, failing to falsify a hypothesis does not prove that hypothesis: it remains provisional. However, a hypothesis that has been rigorously tested and not falsified can form a reasonable basis for action, i.e., we can act as if it were true, until such time as it is falsified. Just because we've never observed rain falling upward, doesn't mean that we never will—however improbable, our theory of gravity may be falsified some day.
Popper's view is not the only view on evaluating hypotheses. For example, some forms of empiricism hold that under a well-crafted, well-controlled experiment, a lack of falsification does count as verification, since such an experiment ranges over the full scope of possibilities in the problem domain. Should we ever discover some place where gravity did not function, and rain fell upward, this would not falsify our current theory of gravity (which, on this view, has been verified by innumerable well-formed experiments in the past) – it would rather suggest an expansion of our theory to encompass some new force or previously undiscovered interaction of forces. In other words, our initial theory as it stands is verified but incomplete. This situation illustrates the importance of having well-crafted, well-controlled experiments that range over the full scope of possibilities for applying the theory.
In recent years, philosophers of science have tried to integrate the various approaches to
evaluating hypotheses, and the scientific method in general, to form a more complete system that integrates the individual concerns of each approach. Notably, Imre Lakatos and Paul Feyerabend, colleague and student, respectively, of Popper, have produced novel attempts at such a synthesis.
[edit] Hypotheses, Concepts and Measurement
Concepts, as abstract units of meaning, play a key role in the development and testing of
hypotheses. Concepts are the basic components of hypotheses. Most formal hypotheses connect concepts by specifying the expected relationships between concepts. For example, a simple relational hypothesis such as “education increases income” specifies a positive relationship between the concepts “education” and “income.” This abstract or conceptual hypothesis cannot be tested. First, it must be operationalized or situated in the real world by rules of interpretation. Consider again the simple hypothesis “Education increases Income.” To test the hypothesis the abstract meaning of education and income must be derived or operationalized. The concepts
should be measured. Education could be measured by “years of school completed” or “highest degree completed” etc. Income could be measured by “hourly rate of pay” or “yearly salary” etc. When a set of hypotheses are grouped together they become a type of conceptual framework. When a conceptual framework is complex and incorporates causality or explanation it is
generally referred to as a theory. According to noted philosopher of science Carl Gustav Hempel “An adequate empirical interpretation turns a theoretical system into a testable theory: The hypothesis whose constituent terms have been interpreted become capable of test by reference to observable phenomena. Frequently the interpreted hypothesis will be derivative hypotheses of the theory; but their confirmation or disconfirmation by empirical data will then immediately strengthen or weaken also the primitive hypotheses from which they were derived.”[7]
Hempel provides a useful metaphor that describes the relationship between a conceptual
framework and the framework as it is observed and perhaps tested (interpreted framework). “The whole system floats, as it were, above the plane of observation and is anchored to it by rules of interpretation. These might be viewed as strings which are not part of the network but link certain points of the latter with specific places in the plane of observation. By virtue of those interpretative connections, the network can function as a scientific theory”[8] Hypotheses with concepts anchored in the plane of observation are ready to be tested. In “actual scientific practice the process of framing a theoretical structure and of interpreting it are not always sharply
separated, since the intended interpretation usually guides the construction of the theoretician.”[9] It is, however, “possible and indeed desirable, for the purposes of logical clarification, to
separate the two steps conceptually.”[9]