What do we know?

We are usually told that "knowledge is justified true belief". This is actually the ancient, Platonic concept of knowledge (see Plato's dialog Cratylus 385 b 2; and Sophist 263 b). Surprisingly, it is still taken seriously in philosophy and other scholarly fields today, despite its highly problematic character. For details, see ([1], pp. 480 ff.).

What is called knowledge, however, has little to do with justifiedness and truth. Most of what we know or believe, we know or believe because someone told us so, that is, we learned it from the written or spoken words of others, from testimony in the widest sense. Consider, for instance, your belief that you were born on a particular date in a particular place. You believe this is true because you hold a birth certificate in your hands that originates from a particular city authority and carries your name and those data. Your belief is a testimonial belief on the grounds that it is based on the certificate as a written testimony. Interestingly, the testimony provided by the city authority is based itself on another testimony that stems from your parents or their proxy, or from the hospital where you may have been born, who told the city authority the story of your birth. That means that if experience, memory, and reasoning are our primary individual sources of knowledge, testimony is our primary social source of knowledge. And without this social source of knowledge, with regard to intellect human beings would not be so very distant from animals, and scientific knowledge would not exist at all. Consider another example:

You believe that increased levels of blood cholesterol cause atherosclerosis, which may lead to diseases such as stroke and myocardial infarction, and therefore you follow, or try to follow, a particular dietary regimen to prevent high cholesterol levels in your blood and body. You yourself have not investigated the pathobiochemical effects of elevated cholesterol levels. Nor have you analyzed the metabolic advantages of the specific dietary regimen you are following. You have only been told, by written or spoken testimony, about what these effects and advantages may be.

In exactly the same manner, most of the information provided by a scientific publication stems from other literature sources or persons, i.e., from testimony. Testimony can exist in indefinitely long chains. As in the example above about how you came to know the date and place of your birth, a testifier herself may know something on the basis of a testimony by a third testifier, while this third party knows it on the basis of testimony by a fourth, and so on. However, the chain must end in some initial source so as to avoid both an infinite regress and a vicious circle. Surprisingly, the origin of the chain, that is, the initial source of testimonial knowledge, is not 'experience, memory, and reasoning' as one would suppose, but a community, i.e., the society. For details of this communitarian theory of knowledge, see ([1], pp. 536-550).

[1] Sadegh-Zadeh K. Handbook of Analytic Philosophy of Medicine. Dordrecht: Springer, 2015.