We have next to consider who the “all” are, whose happiness is to be taken into account. Are we to extend our concern to all the beings capable of pl… - Henry Sidgwick

Is it total or average happiness that we seek to make a maximum?...we foresee as possible that an increase in [population] numbers will be accompanied by a decrease in average happiness...if we take Utilitarianism to prescribe, as the ultimate end of action, happiness on the whole...it would follow that, if the additional population enjoy on the whole positive happiness, we ought to weigh the amount of happiness gained by the extra number against the amount lost by the remainder. So that, strictly conceived, the point up to which, on Utilitarian principles, population ought to be encouraged to increase, is not that at which average happiness is the greatest possible...but that at which the product formed by multiplying the number of persons living into the amount of average happiness reaches its maximum.

I may begin by laying down as a principle that ‘all pain of human or rational beings is to be avoided’; and then afterwards may be led to enunciate the wider rule that ‘all pain is to be avoided’; it being made evident to me that the difference of rationality between two species of sentient beings is no ground for establishing a fundamental ethical distinction between their respective pains.

[T]he history of thought […] reveal[s] discrepancy between the intuitions of one age and those of a subsequent generation. But where the conflicting beliefs are not contemporaneous, it is usually not clear that the earlier thinker would have maintained his conviction if confronted by the arguments of the later. The history of thought, however, I need hardly say, affords abundant instances of similar conflict among contemporaries; and as conversions are extremely rare in philosophical controversy, I suppose the conflict in most cases affects intuitions—what is self-evident to one mind is not so to another. It is obvious that in any such conflict there must be error on one side or the other, or on both. The natural man will often decide unhesitatingly that the error is on the other side. But it is manifest that a philosophic mind cannot do this, unless it can prove independently that the conflicting intuitor has an inferior faculty of envisaging truth in general or this kind of truth; one who cannot do this must reasonably submit to a loss of confidence in any intuition of his own that thus is found to conflict with another’s.