I chose to conclude my book with the notion of rationality. This is because I consider mathematics and science products of rational thinking. Thus, to behave rationally implies to behave according to the recommendations of science. (For example, to avoid smoking. It took some centuries to find out that smoking is dangerous to our health. Other examples are to avoid junk food and to do physical exercises.) One should remember that science keeps changing through time. Thus, being rational in the twenty-first century is different from being rational in the days of Newton.
But rationality is more than that. Here is an excerpt from Merriam-Webster’s characterization of rational: “To be rational is to be reasonable. Rationality is the quality or state of being agreeable to reason. Rationality is applied to opinions, beliefs and practices.” About being reasonable, the dictionary adds that reasonable is “not extreme or excessive” and it is “moderate and fair.”
Wikipedia’s description of rational includes: “generally positive attributes, including: reasonable, not foolish, sane and good.”
Both Merriam-Webster and Wikipedia agree that rationality, in ordinary language, also has a moral aspect (moderate, fair, and good). Be fair! Be considerate! Be a human being!