IN THE FOLLOWING DISCUSSION WE ARE CONCERNED WITH tolerance, not as a physical problem, but as a problem of human relations. In this context, ‘to tolerate’ generally means to endure, suffer or put up with a person, activity, idea or organization of which or whom one does not really approve. One can ‘put up with’ an item both when one can and cannot do anything about it. For example, one can ‘put up with’ the excesses of a ruler whose behaviour one has no power to amend. Equally, one can ‘put up with’ the excesses of a child even where one has no need to do so. In the second case, one has control; in the first, one does not. Both cases could be advanced as instances of ‘tolerance’. But cases of the first sort (powerlessness) I shall label as instances of ‘acquiescence’ or ‘sufferance’ or ‘endurance’, since it is obvious that acquiescence typically flows from powerlessness. I shall label cases of the second sort (powerfulness) as instances of tolerance. It is clear in any event that these two types of case are distinct, and, for the purposes of this discussion, at least, differential labelling is essential. In this context, an agent will be said to ‘tolerate’ an item where the item is disliked or disapproved and is yet voluntarily endured. On this definition it is plain that tolerance requires some form of self-restraint by the tolerator.