Can the law of nature be changed?

It seems that the law of nature can be changed:

Objection 1:  The Gloss on Ecclesiasticus 17:9 (“He gave them instructions, and the law of life”) says, “He wished law of the letter to be written in order to correct the natural law.”  But what is corrected is changed.  Therefore, the natural law can be changed.

Objection 2:  The killing of the innocent is contrary to the natural law, as are adultery and theft as well.  But these have been changed by God, viz., (a) when God commanded Abraham to kill his innocent son, according to Genesis 22:2; (b) when He commanded the Jews to steal the vases they had borrowed from the Egyptians, according to Exodus 12:35; and (c) when He commanded Hosea to take a prostitute as his wife, according to Hosea 1:2.  Therefore, the natural law can be changed.

Objection 3:  In Etymologia Isidore says, “The communal possession of all things and equal liberty belong to natural law.”  But we see that these have been changed through human laws.  Therefore, it seems that the natural law is changeable.

But contrary to this:  Decretals, dist. 5, says, “The natural law derives from the very beginnings of the rational creature.  Neither does it change over time, but remains immutable.”

I respond:  There are two ways to understand what it is for the natural law to be changed.
First, it is changed by something’s being added to it.  In this sense nothing prevents the natural law from being changed.  For many things useful to human life have been added to the natural law, both by the divine law and also by human laws.
Second, the natural law might be thought of as being changed by way of subtraction—so that, namely, something that was previously in accord with the natural law ceases to belong to the natural law.  Given this sense of change, the law of nature is altogether unchangeable with respect to its first principles.  Now with respect to its secondary precepts, which we have claimed to be, as it were, particular conclusions in the neighborhood of the first principles, the natural law is not changed so as to prevent its always being the case that what the natural says is right in the preponderance of particular cases.  However, in a few cases, as was explained above (a. 4), it can be changed in some particular because of special causes that obstruct the observance of secondary precepts.

Reply to objection 1:  The written law is said to have been given in order to correct the law of nature either because (a) what the natural law is lacking was supplied by the written law, or because (b) the law of nature had in certain respects been corrupted in the hearts of some to such an extent that they took what was naturally bad to be good, and this sort of corruption needed correction.

Reply to objection 2:  Everyone in general, both the innocent and the guilty, dies by natural death, and according to 1 Kings 2:6 (“The Lord gives death and gives life”), natural death is imposed by God’s power because of Original Sin.  And so by God’s command death can be inflicted without any injustice on any man, whether guilty or innocent.
Similarly, adultery is sexual intercourse with someone else’s wife, who was sworn to that other man by a divinely given law.  Hence, for someone to be intimate with any woman by God’s command is neither adultery nor fornication.
The same holds for theft, which is the taking of what belongs to another.  For whatever someone takes at the command of God, who is the owner (dominus) of the universe, is such that he is not taking it against the owner’s will—which is what theft is.
And not only is it the case that whatever is commanded by God in human affairs is by that very fact just, but also, as was explained in the First Part (ST 1, q. 105, a. 6), whatever is done by God among natural things is in some sense natural.

Reply to objection 3:  There are two ways in which something is said to belong to the natural law (esse de iure naturali).
First, something is said to belong to the natural law because nature inclines one toward it, e.g., that one should not harm another.
Second, something is said to belong to the natural law because nature has not induced the contrary.  For instance, we could say that it belongs to the natural law that man is unclothed, since nature does not give him clothes, but instead human art invented them.
It is in the second sense that a communal possession of all goods and equal liberty for all are said to belong to the natural law—since, namely, servitude and the distinctions among possessions are induced not by nature but by men’s reason because of their usefulness to human life.  And so on this score the law of nature has not been changed except by addition.