This blog post examines how scientific knowledge is generated through the processes of verification and falsification, and how empirical evidence defines science.
How is scientific knowledge generated? Explanations for this can vary depending on the philosophical perspective on science. One such perspective is logical positivism, which judges the meaning of scientific statements based on empirical verifiability. This perspective emphasizes that scientific knowledge is accumulated solely based on empirical evidence. Logical positivists consider scientific statements meaningful only if they can be empirically verified; statements that cannot be verified are deemed unscientific or meaningless. Let us examine the process of generating scientific knowledge from a logical positivist perspective through the study of salmon migration.
Scientists wanted to understand how salmon return to their birthplace. Native Americans believed salmon returned due to supernatural forces. However, scientists considered such explanations scientifically meaningless because they could not be empirically verified. This aligns with the logical positivist critique that supernatural explanations cannot be objectively confirmed through empirical verification. Therefore, scientists began to exclude supernatural explanations and focus solely on verifiable hypotheses. Scientists devised explanatory methods such as the visual hypothesis, the Earth’s magnetic field hypothesis, and the olfactory hypothesis.
To test the visual hypothesis, scientists caught and tagged salmon arriving at two rivers in the American Northwest, the Issaquah and the Fork. They then divided the caught salmon into two groups. One group had their eyes covered. The other group was not blindfolded. Both groups of salmon were released into freshwater further downstream than the point where the two rivers meet. The experiment showed little difference in the number of salmon returning to their capture site between the two groups.
This result indicated that the visual hypothesis was not supported. Through this experiment, scientists were able to draw the important conclusion that salmon homing does not rely solely on visual information. However, the rejection of one hypothesis does not mean the research ends. Scientific inquiry progresses through the process of finding alternative hypotheses and repeating experiments. Inspired by the idea that pigeons use the Earth’s magnetic field to find their way home, scientists considered the hypothesis that salmon also utilize the Earth’s magnetic field. However, the experimental results did not support the geomagnetic field hypothesis.
After the geomagnetic hypothesis also failed, scientists began exploring other possibilities. During this process, the hypothesis that salmon olfaction could play a crucial role was proposed. To test this olfactory hypothesis, inspired by eel research, scientists conducted experiments using the same method as the visual hypothesis tests. They caught salmon from two rivers, placing nose plugs on one group and leaving the other group unplugged. After releasing these salmon, they recaptured them at the original capture sites as they swam upstream to spawn in freshwater. They classified the recaptured salmon based on whether they had nose plugs and their original capture location. Comparing these results with the deduced outcomes, scientists found the hypothesis was statistically supported.
Many scientists generate new knowledge through this process. First, they encounter a puzzling phenomenon that current knowledge cannot explain. This puzzle sparks a desire to explain it. Then, based on prior knowledge of similar situations, they formulate a tentative explanation. A crucial point here is that a scientific hypothesis must be presented in a testable form; it cannot be a mere conjecture. A hypothesis that cannot be tested is not a valid subject for scientific inquiry. Next, they devise methods to test the tentative explanation. They then collect data and compare it with the results deduced from the tentative explanation. If the hypothesis is not supported, this process is cyclically repeated, and new scientific knowledge emerges as the result of this iterative cycle. At this stage, the hypothesis is verified through experiments and observations, making it highly significant. This is why logical positivists set verifiability as a key criterion for distinguishing science from non-science.
Ultimately, scientific knowledge develops progressively through a continuous process of verification and falsification. Verified hypotheses are temporarily accepted but can be modified at any time by new evidence. This process demonstrates that science is a discipline that constantly self-corrects in pursuit of truth.
