On the Letters of Others

671. The secret of letters. To open the letters of others, or to read them when opened and secretly kept, is of itself a sin from its kind grave against justice: for anyone has a strict right to his own secret. But smallness of matter is given in this thing; therefore if someone were to read letters which he prudently supposes contain only matters of light moment, he would not sin gravely.

To collect letters torn into tiny pieces and thrown into a public place, and to read them after putting together the fragments, is probably not against justice; yet if the letters contain anything whose revelation would turn to the detriment of the owner, that must be kept hidden from charity, under grave or light obligation according to the measure of the damage.

St. Alphonsus indeed (n. 70) judges it more probable that one who reads the fragments after putting them together sins against justice, because letters are torn up so that they cannot be read, and therefore the tearing is a sign that the owner wishes to reserve to himself the right over the secret which is contained in the letters. Lugo, on the contrary (disp. 14, n. 151), judges that the reader does not sin against justice, because casting into a public place is a sign that the owner yields his right over the letters cast out, whose reading he cannot impede; but they are torn up in order that the reading may be made more difficult.

672. Permission to open the letters of others. It is lawful to open another's letters or to read them when opened:

a. From tacit consent or consent rightly and deservedly presumed (for example, by reason of friendship) either of him who writes the letters or of him to whom they are written: for each can yield his right over the secret, and therefore thus injury is done to no one.

b. From a rule to which one has freely subjected himself. Therefore regular superiors can licitly open and read the letters of their subjects where either this right is granted them from the rule or has been introduced through legitimate custom. Nevertheless letters which are directed to mediate superiors are excepted, and letters which contain secrets of conscience. If the superior rightly doubts whether the letters truly contain secrets of conscience, he can licitly inspect them; but if they truly contain secrets, he must abstain from reading.

c. From the necessity of averting grave damage from the republic, from subjects, or from oneself. Therefore a. it is lawful for public authority (princes, military leaders) to open letters if sufficient indications are present that this is necessary for consulting the public good. b. It is lawful for a father of a family to read the letters of children who are still under paternal power, and for a superior to read the letters of pupils committed to his care, unless they treat of matters of conscience or contain secrets of the family, because this is judged necessary for consulting the good of the son or subject. c. It is lawful for a private man in particular cases to read another's letters when he rightly and deservedly judges that something is contained in them which would turn to his grave damage (n. 666).

It is not lawful for masters to read the letters of servants, nor for husbands the letters of wives, by reason of servitude or marriage; yet if they judge with moral certitude that something evil is contained in them, this is lawful to them from what has been said above.