Burden of Proof

Expose False Symmetries & Weed Out Spurious Arguments


When two opposing points of view confront each other, it must not be assumed that they are symmetric, i.e. that they are both about equally plausible. That may sometimes occur, but often one side is much less plausible than the other. When one side of the debate is highly implausible and extraordinary, then the burden of proof falls on those who advance that side.

Sommaire en français Lorsque deux points de vue opposés s’affrontent, il ne faut pas supposer que la situation est symétrique, c’est-à-dire que les deux côtés sont à peu près également plausibles. Cela peut parfois se produire, mais souvent l’un des deux côtés est beaucoup moins plausible que l’autre. Lorsqu’un côté du débat est hautement invraisemblable et extraordinaire, le fardeau de la preuve incombe à ceux qui avancent de ce point de vue.

The concept of burden of proof is an important logical tool which allows us to weed out spurious arguments. It does so by exposing the falsehood of alleged symmetry between two opposing arguments or, in some cases, completely inverting the apparent plausibility of the two opposing sides. We say that one of the opposing sides has the burden of proof when they are making a specific assertion which requires substantiation, whereas the other side is simply expressing scepticism.

Those who take an irrational position, whether out of ignorance, confusion or dishonesty, generally fail to take account of this aspect of the debate. Sometimes they argue for symmetry in a situation where in fact there is no symmetry between the opposing sides of the debate. Worse, they may assume, sometimes unconsciously, that the burden of proof falls on the wrong side.

The basic idea here is summed up in several famous quotations. Science educator Carl Sagan, in his famous television programme Cosmos, declared that “extraordinary claims require extraordinary evidence.” The statement by Christopher Hitchens that “what can be asserted without evidence can also be dismissed without evidence” has become known as Hitchens’ Razor. The ancient Greek mathematician and geometer Euclid made a very similar statement, “what has been affirmed without proof can also be denied without proof”, more than two millenia before. Thus, the burden of proof falls upon the person who makes some extraordinary claim. The opponent who merely questions that claim has no such obligation.

I will illustrate using the following three examples.

(1) Does “God” Exist?

An individual claims that “God” exists. However, another individual disagrees, claiming that knowledge of the existence of such an entity is unavailable. Clearly, the burden of proof here falls upon the person making the claim of god’s existence, starting with the obligation of defining what they mean by “God.” In the absence of such definition or proof, anyone who disagrees may simply dismiss the claim and is under no obligation whatsoever to prove the non-existence of the hypothetical god proposed by the claimant. There is no symmetry between the god-hypothesis and the rejection of that hypothesis. In other words, there is no symmetry between theism and atheism.

(2) What Does “God” Say About Sex?

An individual claims to know what “God” wants in some situation. For example, the individual may claim that god abhors sexual behaviour other than heterosexual relations between a man and a woman who are legally married to each other and that all other sexual behaviour is forbidden. However, another individual disagrees, claiming that no such rule is known to apply. Which individual is right? Clearly, the burden of proof falls upon the individual making the assertion about the will of “God” because that assertion requires knowledge of the existence of god, knowledge that god has a will and knowledge of that will itself. Unless the first individual offers some proof in support of their claim, those who disagree may simply dismiss it. There is no symmetry between the two sides of this disagreement.

(3) Do Symbols Communicate Anything?

A government introduces legislation which bans civil servants and public schoolteachers from wearing religious symbols while on duty. Opponents of the proposed law claim that the ban is unnecessary because, in their opinion, such symbols have no significant effect either on users of civil services or on public school pupils. Supporters of the law disagree. On which side should the burden of proof fall? This situation may appear less obvious that the previous two. Perhaps we have a symmetrical situation here, where the competing assertions are about equally plausible, where neither claim is extraordinary?

However, upon closer inspection, any apparent symmetry disappears. Why do some religious believers wear religious symbols? They do so to communicate their religious identity to others, i.e. in order to assert that identity ostentatiously. If such symbols had no effect, believers would not wear them. Pious Christians use the verb “witness” to describe the act of asserting one’s Christian identity by word or by symbol. Why do corporations spend enormous amounts of money on advertising, using symbols, logos, slogans, etc. to promote their products and/or their brand? They do so because advertising works, because such displays influence those who are exposed to them and change their behaviour in some way.

Thus, It is eminently reasonable to expect that religious symbols will have a real effect on those who witness them. Furthermore, we can expect a particularly significant effect if the wearer is a civil servant or schoolteacher on duty, especially if the observer is a child. In fact, some forms of advertising directed at children are forbidden by law, and for good reason. To assert that such symbols would have no effect—or only harmless effect—is an extraordinary claim which can be rejected in the absence of proof of such innocuousness. A precautionary attitude requires that we take the potential effects of religious symbols seriously.


Of course, some extraordinary claims may turn out to be valid, but only if solid supporting evidence is provided. But in the three examples given above, the claimants never succeed in providing such evidence for their extraordinary claim.

Next blog: TBA

One thought on “Burden of Proof”

  1. About sex, the first question you ask a catholic priest should be about the Immaculate Conception. The question is:

    Do you really believe that the Virgin Mary had a child without having sex?

    I believe that it should be very difficult to demonstrate the veracity of this extraordinary claim,

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