The Tribunal is the Diocesan Court which adjudicates the internal legal affairs of the Church in the name of the Diocesan Bishop. The sacramental status of a marriage is one of the internal legal affairs of the Church.
Marriages are investigated by the Tribunal because the Catholic Church recognizes the initial and lawful marriage between a man and a woman as binding. The annulment process begins when one of the parties of such a recognized lawful marriage requests (petitions) the Church to investigate and determine whether that marriage was indeed binding.
A Church annulment has no effects in civil law. As such, any judgment of nullity does not affect the legitimacy of children. The judicial process is to establish the status of persons solely within the Church and to safeguard the rights attributed to the faithful under Church law, which is the Code of Canon Law. Concerning marriages, the process is simply to seek the truth regarding the validity of a marriage.
The intent of the Tribunal is to
seek the truth in all matters which come before it.
When you petition the Tribunal to investigate your marriage for possible invalidity, the final outcome remains unknown until the entire process has been completed and a decision is rendered by the Judges. In the Code of Canon Law, marriage is said to “enjoy the favor of the law” which means that even uncertainty about the validity of a marriage would favor that marriage to be valid. There must be moral certitude on the part of the Judges that a marriage is, without a doubt, invalid in order for an annulment to be granted.
Thus, in order for the Judges to reach moral certitude, there must be a complete and often time-consuming investigation into the relationship of the parties who have given their consent to enter marriage. In justice, the description of that relationship can never be one-sided. Both parties are expected to participate. There may be an occasion where the responding party may not be participating for whatever reason. Should that be the circumstance, it would be absolutely necessary to have relatives or friends of the absent party participate in the process.