Ex post lacto, or, mother’s milk vs the positive law
April 14, 2018 § 43 Comments
If the positive law of some governing body expressly authorized X yesterday, and then that same body criminalizes X tomorrow, it is unjust – with caveats – for that body to punish someone tomorrow for having already done X yesterday. This has to do with the just exercise of authority, not the justice of the action in question: when a particular authority punishes an action which it explicitly authorized this (the punishment) is an unjust act by that authority. If I authorized you to shoot the dog it would be unjust for me to punish you for having already shot the dog, though it is not unjust for me to withdraw authorization.
This principle against ex post facto law has limits. Punishment might not be an unjust act by a different, especially a higher, authority: God punishing people for doing things which are supposedly “authorized1” by the positive law is not unjust, for example. And in general a different authority may be justified in punishing actions which it did not authorize, even though some other authority attempted to “authorize” it.
This is especially true when people ought to know better. Importantly, the fact that some authority has not said anything about X does not constitute authorization by that authority to do X. In this case no ex post facto prohibition applies as a moral constraint on the authority to punish. And I would not be too quick to dismiss the notion that mothers mostly ought to know better than to kill their own children, no matter what pressures they are under.
Modern people with their politically liberal commitments may find this difficult to swallow, but the fact that nobody in authority has expressly forbidden doing X does not mean that you are authorized (have the authority) to do X. The fact that there is no positive law prohibiting you from doing X doesn’t grant you a right to do X, for all possible X: “right” is just a different term for authority.
When we do something which we have no right to do, sometimes there are consequences, including punishment of some sort by someone in authority. And the fact that someone – even someone in authority – told you that you were authorized to do something evil does not confer actual authorization: it doesn’t make you not guilty, it just makes the person(s) who attempted to authorize evil also guilty.
The fact that someone in authority egged you on to commit murder may be a mitigating factor in deciding upon a just punishment. But it can never be entirely exculpatory. We are responsible for our own choices2, and that includes being sure that we have the authority to do the things we choose to do.
 I use scare quotes around “authorize” because in fact nobody has the capacity to authorize or require doing evil.
 Here I leave out the mentally ill and otherwise truly incompetent.