Does a Lack of Evidence Against a Claim Make It True?

“No one has proved it false, so it is true” is commonly described as an appeal to ignorance. The mistake is not admitting that knowledge is missing. It is upgrading “not yet refuted” directly into “confirmed”. A claim and its denial may both temporarily lack adequate support. In that position, suspending judgement is often rational; it does not mean assigning each side an equal probability.

Contemporary argumentation theory also shows that a failure to find something can sometimes provide a reason. What matters is the power of the test. Suppose someone claims that a new office app secretly records audio. Supporting the suspicion only with “you cannot prove it doesn't” is inadequate. If an independent audit checks system permissions, network traffic and recording interfaces and still finds no such behaviour, however, that absence carries more weight. It is not an absolute logical proof. It is a failed search that had a reasonable chance of detecting the target.

The burden of proof is not always divided equally either. A person introducing a specific existence claim normally owes the first reasons. Developers who control code and logs are also better placed than ordinary users to explain what a system does. Risk and the cost of error can raise the standard of evidence, but caution must not be converted into “true until disproved”.

My judgement is that we should ask two questions whenever no counter-evidence appears: was a real search made, and how likely was that search to succeed if the claim were true? Only then can “no evidence” become limited evidence. Otherwise it marks a gap in knowledge.

https://plato.stanford.edu/entries/evidence/
https://iep.utm.edu/fallacy/