The Practice of Science within a Paradigm Theory
"Normal science," Kuhn writes, "consists in the actualization of that promise" to successfully provide problems (and problem-solutions) offered by paradigms. Thus, the purpose of normal science is to, through problem solving, move a paradigm into closer and closer agreement with nature.
This purpose is realized through three activities: the determination of significant fact, matching fact with theory and the articulation of the paradigm.
Selecting Significant Fact
Determination of significant fact means selecting which facts the paradigm implies are to be useful in accurately describing the nature of reality. In biology, for example, some significant facts include (or have at one time included) the identity of the genetic material, the heritability of certain traits and the connection between traits and individual genes. As Kuhn claims for physics and chemistry, the accurate and general determination of these facts occupies a great part of the literature and experimentation of biology, and many biologists have attained recognition for their work because of their successes in accurately determining the base-pair sequence of the Human genome or, especially, the chemical identity of the genetic material.
Connecting Observable and Theoretical Concepts
The second activity of normal science is to link observable facts with predictions deduced from the paradigm in use. Continuing with biology as the example, this activity would include determining the phenotypic effect of a gene introduced into an organism through recombinant DNA technology in order to confirm, say, that expression of the gene does indeed lead to the activation of certain other genes.
Articulating the Paradigm
The third and final activity of normal science as Kuhn has it is the "empirical work done to articulate the paradigm theory". Kuhn considers this to be the most important of the three activities of normal science and divides this articulation into three more categories.
The first includes the determination of the value of universal constants, and Kuhn provides the example of the gravitational constant. As Kuhn writes, Newton's problems could be solved without knowing the value of the constant (in the equations, the constant cancels out), and indeed the gravitational constant was not determined until long after the publication of the Principia. The paradigm of Newtonian mechanics demands the existence of a stable gravitational constant and so its accurate determination contributes to the articulation of the paradigm.
The second class of articulating experiments are those which seek to produce quantitative laws, such as Bernoulli's law relating the pressure of a fluid to its rate of flow. Kuhn believes that without a paradigm (in this case, that of Newtonian mechanics and the differential calculus) it would be impossible for a scientist to suspect that this type of quantitative law could be determined. "So general and close is the relation between qualitative paradigm and quantitative law that...such laws have often been correctly guessed with the aid of a paradigm years before apparatus could be designed for their experimental determination".
The final class of these experiments are those which seek to determine how a paradigm will explain phenomena which are closely related to the one at the center of the paradigm but to which the paradigm might be applied in numerous ways. A example of such a determination (taken from theoretical physics) is the demonstration through Special Relativity that the electrical and magnetic forces are aspects of the same electromagnetic phenomenon.
Kuhn believed that the theoretical work of science falls into nearly the same categories; much theoretical work has the purpose of articulating the theory such that it can be easily tested through experiment. Other theoretical work includes finding what Kuhn calls points of contact between theory and nature. In order to adapt his mechanics for purposes other than the one for which they were originally devised (the explanation of celestial phenomena), for example, Newton was forced to make approximations (such as that of the point mass) and so restrict the agreement between predictions and experiment. Theoretical work in paradigm articulation is closely tied to experimental work in the same area and Kuhn gives the design of Coulomb's experimental apparatus as an example.
Motivation to Problem-Solve
Kuhn argues that these activities are not conducive to the production of novelty or unexpected result. Rather, a paradigm suggests a narrow range of conceivable experimental results and, furthermore, experiments which produce results outside of that range reflect not on the inadequacy of the paradigm but on that of the scientist (for the most part, at least).
Phenomena which do not contribute to the articulation of the paradigm are often ignored, and are relegated to the position of "mere facts". As such, the three activities of normal science must not be motivated by a desire to produce genuinely novel results. According to Kuhn, however, they could be motivated by an addiction to the determination of solutions to what are, for "the proper sort of addict", the fascinating problems a paradigm provides to the practitioner of normal science.