dukkha, in Buddhist thought, the true nature of all existence. Much Buddhist doctrine is based on the fact of suffering; its reality, cause, and means of suppression formed the subject of the Buddha’s first sermon (see Four Noble Truths). Recognition of the fact of suffering as one of three basic characteristics of existence—along with impermanence (anichcha) and the absence of a self (anatta)—constitutes the “right knowledge.” Three types of suffering are distinguished: they result, respectively, from pain, such as old age, sickness, and death; from pleasure changing to pain; and from the fact that, because of impermanence, beings are susceptible to pain in the next moment.