Science is the best way to gain objective knowledge (that is, independent from what others tell us) about the world because its method uses two sources of authority: reason and experience.

However, some people say that science is the only source of trustworthy truth or knowledge. Terry Pratchett falls foul of this fallacy – that science provides the only truth – when he has Death say that belief in the Hogsfather is a small lie that prepares us to believe in the big lies, like love and justice. (The Hogsfather).

There are two problems with the assertion that science is the only source of true knowledge:

1. Can this assertion be proved by science? No it can’t: so why should we accept it as true? It is a belief that has a foundation other than science; either the authority of another person, or from our own rational, logical processes.

2. There are other facts we accept as true without requiring scientific proof. For example, answer the following three questions.
a. Did you exist yesterday?
b. Do you think murder is wrong?
c. Do you love your family?

Whatever your answers to these questions are (presumably they are all “Yes”), is it possible to prove those answers scientifically? No.

Scientific proof requires that what is being tested must be detectable by the senses: it must be tangible; able to be directly measured. With reference to the three questions above, nothing that occurred in the past (history) nor abstract objects such as moral attitudes (right and wrong; justice) or emotional ties (love) can be proven scientifically – it can neither be directly observed nor directly measured. [1]

The fact of past events can be inferred through the existence of items such as financial records, photographs, and minutes of meetings. These items are called documentary, or legal-historical, evidence, and is be used to form an explanation, much as scientific evidence is used to form a theory (that is, an explanation) about something that cannot be observed or measured directly, such as the fact that you had breakfast this morning. To obtain scientific evidence to support this hypothesis, we would measure your metabolism, observe the kind of food in your digestive system (whether it is the kind of food one might have at breakfast) and its state and location, and compare this with what and where we would expect it to be in a standard human digestive system. From these results we would draw a conclusion, which may be that you ingested cereal, toast with jam, and coffee at about 7am local time, which coincides with a daily event in which a great proportion of people participate, and which we call breakfast.

Proof for abstract objects such as beliefs or attitudes is next to impossible to quantify, because they are neither directly observable nor directly measurable. They do not even exist as such: they are relationships, interactions, between objects. For example, the four elemental forces (gravity, electromagnetism, and the strong and the weak nuclear forces) are abstract objects, as are love and justice. With gravity, we observe two objects being drawn towards one another but there is no tangible entity causing this attraction. Therefore we conclude the existence of a force we name gravity. The same applies to love, justice, and other concepts. The interaction between the objects cannot be measured directly but it is nonetheless there. Like gravity, beliefs, attitudes and relationships cannot exist independently; they are how describe the interaction between objects.


[1] An abstract – intangible – object stands in apposition to a concrete – tangible – one.