[1] The notion of "reasonableness" is omnipresent in European law, and has also affected "international treaties and general customs".
[4] Examples of its use can be found in canon and medieval law, suggesting roots going back to Ancient Rome.
[12][13][14] According to Paul Craig, it is "concerned with review of the weight and balance accorded by the primary decision-maker to factors that have been or can be deemed relevant in pursuit of a prima facie allowable purpose".
The scale of reasonability represents a quintessential element of modern judicial systems and is particularly important in the context of international disputes and conflicts of laws issues.
The concept is founded on the notion that all parties should be held to a reasonable standard of conduct[citation needed] and has become embedded in a number of international conventions such as the UNIDROIT principles[17] and the CISG.