It may however be urged that this variation of custom is no obstacle to the definition of duty, because we may lay down that the customs of any society ought to be obeyed so long as they are established, just as the laws ought, although both customs and laws may be changed from time to time. And no doubt it is generally expedient to conform to established customs: still, on reflection, we see that it cannot be laid down as an absolute duty. For the cases of Custom and Law are not similar: as in every progressive community there is a regular and settled mode of abrogating laws that are found bad: but customs cannot be thus formally abolished, and we only get rid of them through the refusal of private individuals to obey them; and therefore it must be sometimes right to do this, if some customs are vexatious and pernicious, as we frequently judge those of antique and alien communities to be. And if we say that customs should generally be obeyed, but that they may be disobeyed when they reach a certain degree of inexpediency, our method seems to resolve itself into Utilitarianism: for we cannot reasonably rest the general obligation upon one principle, and determine its limits and exceptions by another. If the duties above enumerated can be referred to independent and self-evident principles, the limits of each must be implicitly given in the intuition that reveals the principle.
§ 4. In order then to ascertain how far we possess such principles, let us examine in more detail what Common Sense seems to affirm in respect of these duties.
They seem to range themselves under four heads. There are (1) duties arising out of comparatively permanent relationships not voluntarily chosen, such as Kindred and in most cases Citizenship and Neighbourhood: (2) those of similar relationships voluntarily contracted, such as Friendship: (3) those that spring from special services received, or Duties of Gratitude: and (4) those that seem due to special need, or Duties of Pity. This classification is, I think, convenient for discussion: but I cannot profess that it clearly and completely avoids cross divisions; since, for example, the principle of Gratitude is often appealed to as supplying the _rationale_ for the duties owed by children to parents. Here, however, we come upon a material disagreement and difficulty in determining the maxim of this species of duty. It would be agreed that children owe to their parents respect and kindness generally, and assistance in case of infirmity or any special need: but it seems doubtful how far this is held by Common Sense to be due on account of the relationship alone, or on account of services rendered during infancy, and how far it is due to cruel or neglectful parents. Most perhaps would say, here and in other cases, that mere nearness of blood constituted a certain claim: but they would find it hard to agree upon its exact force.[195]