As stated above, the church, like the state, has certain requirements before its members can marry . Both church and state are concerned that marriages be stable. The well being of society depends on this. If any of these major requirements are lacking the grounds for annulment can be investigated. Two areas for investigation are impediments and consent.
Impediments are obstacles to a couple getting married .
Unless these have been dealt with prior to the wedding, then some of them could invalidate a marriage. There are a variety of impediments. Some have to do with previous relationships such as a previous marriage, blood relationships, etc. Others have to do with differences of religion and sex. A third category has received a lot of publicity in the recent past.