Acceptability is the characteristic of a thing being subject to acceptance for some purpose. A thing is acceptable if it is sufficient to serve the purpose for which it is provided, even if it is far less usable for this purpose than the ideal example. A thing is unacceptable if it deviates so far from the ideal that it is no longer sufficient to serve the desired purpose, or if it goes against that purpose. From a logical perspective, a thing can be said to be acceptable if it has no characteristics that make it unacceptable: Hungarian mathematicianImre Lakatos developed a concept of acceptability "taken as a measure of the approximation to the truth". This concept was criticized in its applicability to philosophy as requiring that better theories first be eliminated. Acceptability is also a key premise of negotiation, wherein opposing sides each begin from a point of seeking their ideal solution, and compromise until they reach a solution that both sides find acceptable: Where an unacceptable proposal has been made, "a counterproposal is generated if there are any acceptable ones that have had already been explored". Since the acceptability of proposition to a participant in a negotiation is only known to that participant, the participant may act as though a proposal that is actually acceptable to them is not, in order to obtain a more favorable proposal.
Acceptable risk
One concept of acceptability that has been widely studied is acceptable risk in situations affecting human health. The idea of not increasing lifetime risk by more than one in a million has become commonplace in public health discourse and policy. It is a heuristic measure. It provides a numerical basis for establishing a negligible increase in risk. Environmental decision making allows some discretion for deeming individual risks potentially "acceptable" if less than one in ten thousand chance of increased lifetime risk. Low risk criteria such as these provide some protection for a case where individuals may be exposed to multiple chemicals e.g. pollutants, food additives or other chemicals. In practice, a true zero-risk is possible only with the suppression of the risk-causing activity. Stringent requirements of 1 in a million may not be technologically feasible or may be so prohibitively expensive as to render the risk-causing activity unsustainable, resulting in the optimal degree of intervention being a balance between risks vs. benefit. For example, emissions from hospital incinerators result in a certain number of deaths per year. However, this risk must be balanced against the alternatives. There are public health risks, as well as economic costs, associated with all options. The risk associated with no incineration is potential spread of infectious diseases, or even no hospitals. Further investigation identifies options such as separating noninfectious from infectious wastes, or air pollution controls on a medical incinerator.
Acceptable variance
Acceptable variance is the range of variance in any direction from the ideal value that remains acceptable. In project management, variance can be defined as "the difference between what is planned and what is actually achieved". Degrees of variance "can be classified into negative variance, zero variance, acceptable variance, and unacceptable variance". In software testing, for example, "enerally 0-5% is considered as acceptable variance" from an ideal value. Acceptance testing is a practice used in chemical and engineering fields, intended to check ahead of time whether or not a thing will be acceptable.
