What is the proper consent for marriage these days? How do you know that there has not been a defect of consent? There have been thousands of marriage annulments, granted years after the ceremony has taken place, where they claim some defect in consent.
Marriages are presumed to be valid until show to be otherwise, so one is never completely certain that it could not be anulled (until death that is), or for the baptised, that it is a sacrament. (We cannot read minds.)
The object of marital consent, the self-gift of the spouses, has the following three essential elements: exclusivity, permanence, and granting the natural conjugal act apt to the creation of children (it is not necessary to be fertile).
The consent must truthfully be given freely by the man and woman, both capable of granting the object, with understanding of what the marriage covenant is, without fraud or misrepresentation of identity, and fulfilling any current conditions to consent.
Some examples that would invalidate a marriage consent: one or other spouse intends to not be exclusive, or intends the marriage to be temporary, or intends to not grant conjugal rights.
These are the grounds for anullment from the Latin canon law (CIC):
Lack of Sufficient Use of Reason (canon 1095, 1°)
Grave Defect of Discretion of Judgment (canon 1095, 2°)
Inability to Assume the Essential Obligations of Marriage (canon 1095, 3°)
Ignorance of marriage object or subject (canon 1096)
Error Concerning the Person (identity) (canon 1097, §1)
Error Concerning a Quality of the Person (canon 1097, §2)
Fraud or Imposed Error (canon 1098)
Error Concerning the Unity or Indissolubility of Marriage (Error of Law or Determining Error) (canon 1099)
Error Concerning the Sacramental Dignity of Marriage (Error of Law or Determining Error) (canon 1099)
Total Simulation of Marriage (canon 1101)
Partial Simulation of Marriage (canon 1101)
Conditional Consent – Future Condition (canon 1101, §1)
Conditional Consent – Past and Present Condition (canon 1101, §2)
Force or Grave Fear (canon 1103)
Invalid Convalidation of Marriage (canons 1156-1165)