A civil marriage by itself is NOT considered valid by the Catholic Church, but children of these marriages are still legitimate because legitimacy is a civil, not religious designation. The idea of a civil or non-Catholic marriage being ‘blessed’ by the Church is a misconception. These couples (after proper preparation) actually have to marry each other again, although Church-wise it is really the first time since they didn’t receive the Sacrament before.
In America, in spite of ‘the separation of church and state’ churches are allowed to perform the requirements for a civil marriage. In Mexico, there is true separation and couples must actually have 2 separate ceremonies, civil and church, because priests are not allowed to act as agents of the state.
I suppose things might have been different 50 years ago, but at least 20 years ago it was/is required that the couple get a marriage license issued by the state. This is brought to the priest ahead of time or the ceremony will not be allowed. This is what is signed by the couple, priest, and witnesses and filed with the courthouse. That is the civil part of the marriage. This is done in conjunction with the church ceremony, where you and your spouse conferred the Sacrament of Matrimony upon each other.
Even if for any reason someone believes they or their spouse were not capable of the Sacrament at the time of the wedding, the marriage is still considered to be valid and Sacramental, unless one requests an annulment and the whole process is completed and comes to the same conclusion.
O2
“In America, in spite of ‘the separation of church and state’ churches are allowed to perform the requirements for a civil marriage.”
In America, in spite of ‘the separation of church and state’ it is illegal in many states to perform a wedding ceremony and declare someone married without the permission of the civil authorities. Makes me wonder what a lot of faiths would do if the state refused to grant permission to them, perhaps as a punishment for not accepting the state’s ever mutating version of marriage.
Freegards
IOW, the Catholic church doesn't recognize a non-Catholic marriage, therefore all non-Catholics marriages are just people living in sin.
That is the only option if it's not a legitimate marriage or not recognized as a marriage.