3. The kind and quantity of obligation imposed by any particular law may be gathered from the express mind of the lawgiver. If the matter be capable of a grave obligation, and in making the law words indicating a strict precept are used e.g., we command, we severely ordain the presumption is that the law imposes a grave moral obligation. The same may be said if a grave censure or other grave penalty is imposed on transgressors. The interpretation of Doctors, and the way in which custom interprets a law, are also guides to its binding force.
4. An affirmative law, which commands something to be done, is said to bind always but not for always. Thus we are commanded to pray always i.e., never to abandon prayer though we are not obliged continually to pray all day long, but only at suitable times. A negative precept, on the other hand, binds always and for always, so that we must continually act according to its prescriptions. At no time on days of obligation may we do servile work.
5. A law imposes in the first place an obligation on those subject to it to inform themselves of its existence and provisions, for it imposes the duty of observing it, and this cannot be done unless the terms are known; knowledge of the law is the necessary means to the end. A law also forbids us to put ourselves in the proximate occasion of transgressing it, for the avoidance of such proximate occasions is also a necessary means for the observance of the law.
6. A negative law is observed by abstaining from what is forbidden, for that is the intention of the lawgiver. Provided that we abstain from servile work on a Sunday, we fulfil that part of the law; no special intention of riot working or of fulfilling our obligation is required. An affirmative law which prescribes something to be done sometimes requires a conscious human act for its fulfilment; sometimes it does not. If the obligation be merely real, as the duty of paying a debt, even unconscious payment will suffice, provided that the creditor gets what belongs to him. If a personal obligation is imposed of performing some action e.g., hearing Mass the action must be performed in a human manner, by a conscious, voluntary act. It is not, however, necessary to intend to fulfil the purpose of the law; we satisfy the precept of hearing Mass by intending to hear it and actually doing so; to fulfil the obligation it is not necessary to intend to honour God, nor even to be in a state of grace; the end of the precept does not fall under the precept, as the adage has it.
