"Sui Juris" Latin expression Explained

The latin expression "sui juris" commonly indicates the "capacity to contract in law".

The legal dictionary definitions seem to repeat a common classical theme:

1) To make a valid contract, a person must, in general, be sui juris,

2) Every one of full age is presumed to be sui juris,

3) One who has all the rights to which a freemen is entitled, may contract,

4) one who is not under the power of another, as a slave, a minor, and the like, may contract.

The term is obviously somewhat archaic. In most situations, it lacks meaning based upon its own definition and the requirements envisaged by that definition. Today, it just seems to mean "one who possesses the legal capacity to contract". That would preclude minors, those suffering from significant mental incapacity, bankrupts, those confined in prison (for certain matters) and so on.

However, have a closer look at some of those requirements. You had to be free. You could not be someone's slave. Of course, that was true, but that is no longer the case.

It is interesting that from an historical perspective, an agent need not be "sui juris", at least that was in the old days. And, by the "old days", I mean Roman times. Let's have a look at what "sui juris" meant in those days.

Persons were either independent (sui juris) or dependent (alieni juris). Someone who reached that status of being an independent person in Rome had the right to be the head of their own family. There were all kinds of rules related to dependence.

A son remained dependent until he left home. When he finally left, this emancipation freed him and accorded to him the right to become the head of his own family.

If you were the member of a family, you were not "sui juris", you were a dependant. A son who remained in his father's house, and had children and those children had children, all remained as dependents. There was truly only one head of the household. Oddly, this rule only applied to sons. The children of daughters were dependent upon their own fathers.

This was also a time when slavery was permissible. So, all the slaves were dependent unless granted their freedom.

There was no restriction imposed upon women. They too could be "sui juris" and have the same status as men. In Rome, while husbands preferred to dominate their wives, fathers preferred that their own daughters not be dominated. 

The subordination of women to their fathers was commonplace in ancient civilizations. The subordination of wives to their husbands is of relatively modern vintage and recent jurisprudence. When I say recent, I mean the last 1,000 years or so. 

If you didn't leave home, it was difficult to become "sui juris". However, there were a few other ways, the death of the "sui juris" parent, the loss of Roman citizenship, special honours by Rome, becoming a prisoner of war, and a number of other particular circumstances led to one's freedom.

If you were free, you could enter into any kind of a contract without anyone's approval.

Naturally, as slavery was abolished, the term "sui juris" lost some of its meaning in law. But, it still stands for the basic principle of "freedom to contract".

Agents did not need to be "sui juris", they could negotiate on behalf of their masters and bring their masters into contractual arrangements with others.