1.5: Deductive Reasoning
Deductive reasoning, or deduction, is the type of logic used in hypothesis-based science. In deductive reasoning, the pattern of thinking moves in the opposite direction as compared to inductive reasoning, which means that it uses a general principle or law to predict specific results. From those general principles, a scientist can deduce and predict the specific results that would be valid as long as the general principles are valid.
For example, a researcher can deduce specific predictions from the induced hypothesis "butterflies are attracted to specific flowers based on the petal color". These deductive tests are often formulated as "If...then" statements: if the hypothesis is true, then changing the flower's petal color should alter the butterfly's attraction, but changing its scent or its petal shape should not. Such predictions are used to set up experiments to test the hypothesis.
Although deductive reasoning is at the heart of hypothesis-driven science, and inductive reasoning is mostly associated with descriptive science, both forms of logic are integral to research and often tie together within the same experiments. Following the above example, the researcher might observe that butterflies also tend to avoid flowers with pointed petals. This observation can lead to a new inductive hypothesis, which can then be tested deductively.
Part of this text is adapted from Openstax, Biology 2e, Section 1.1: The Science of Biology
Clark, M. A., Douglas, M., Choi, J. Section 1.1: The Science of Biology. In Biology 2e. OpenStax. Houston, TX (2018).