This letter is a follow-up from the doctoral student who wrote last Monday.  I’ve paraphrased a little just for brevity.


Thanks for your response -- that helped.  Let me ask one of my remaining questions.

You’ve stressed that although the Ten Commandments are a good summary of natural law, they are the kind of summary in which the part stands for the whole -- each commandment stands for a whole category of rights and wrongs.  For example, although they mention only the worst kind of lying, bearing false witness, this is a placeholder for lying in general, and although they mention only the worst kind of sexual impurity, adultery, this is a placeholder for sexual impurity in general. 

Here is my question:  Is there anything in natural law that doesn’t fall under one of these ten categories?  Or would you say that natural law includes exactly the ten kinds of thing that the Decalogue addresses, albeit in a more capacious way?


I would say the latter.  To put it another way, the Ten Commandments are a complete summary of natural duty.

There is a slight complication here, because these Ten have traditionally been enumerated in two different ways.  If we enumerate them the way Thomas Aquinas did, then the first three commandments put man in proper order in his relations to God.  Fidelity, owed God in deeds, is represented by the first commandment, “You shall have no other gods before me.”  Reverence, owed Him in words, is represented by the second, “You shall not take the name of the Lord your God in vain.”  And service, owed Him in thoughts, is represented by the third, “Observe the Sabbath day, to keep it holy.”

The rest of the commandments put man in proper order in his relations with his neighbors, who live with him under God.  First come particular duties, the payment of debts:  These are represented by the fourth commandment, “Honor your father and your mother.”   Next come general duties, that is, the duties to refrain from harming others by deed, word, or thought.  But these need to be subdivided.

The broadest category is the prohibition of harm by deed.  Harm by deed concerning another’s existence is represented by the fifth commandment, “Thou shalt not kill”; concerning the propagation of offspring, by the sixth commandment, “Neither shall you commit adultery”; and concerning another’s possessions, by the seventh commandment, “Neither shall you steal.”

The next category is prohibition of harm by word, represented by the eighth commandment, “Neither shall you bear false witness against your neighbor.”

Finally comes the prohibition of harm by thought, whether through the lust of the flesh, represented by the ninth commandment, “Neither shall you covet your neighbor’s wife,” or through the lust of the eyes, represented by the tenth commandment, “and you shall not desire your neighbor’s house, his field, or his manservant, or his maidservant, his ox, or his ass, or anything that is your neighbor’s.”

It seems that the natural law covers these same ten categories – fidelity, reverence, and service to God; and to our neighbors, the payment of debts, avoiding harm by deeds concerning life, procreation, and property, avoiding harm by word, and avoiding harm by though through the lust of either the flesh or the eyes.  I discuss these at greater length in my online Companion to the Commentary, which is the free online supplement to my Commentary on Thomas Aquinas’s Treatise on Law.

I can’t think of anything that the ten categories overlook.  However, we must take care not to construe them too narrowly.  For example, someone might say that the wrong of transhumanism – of trying to change human nature, say by rewiring our brains, or by blending the genomes of humans and animals -- doesn’t fall under any of the ten categories.  But I would say it falls clearly under the duty of reverence in deeds to God, the Creator.