CathInfo.com

Matrimonial consent is valid only when the intention predominates to transfer (and not positively exclude) the perpetual and exclusive and continual right ot natural intercourse. A condition designed to exclude this transference perpetually or for a certain time or after a certain time (e.g. periodic continence or the non-use except for infertile days or the right only to onanistic relations) is contrary to the substance of marriage, vitiates the consent and invalidates the contract. If this right is transferred and the condition implies only the intention to abuse this transferred right, the contract is valid, as the sinful condition is not contrary to the substance of marriage.

If a restriction made on marital intercourse is absolute, without any limit of time, i.e., the marital right and obligation would be perpetually abused, the presumption (in the external forum) is that the right itself, i.e., the order to the object of the contract, is excluded and thus no true marital consent and valid contract exists. This is especially true if a mutual pact has been made acceding to this condition. If the condition is not absolute but limited to a certain time when this marital abuse is intended, the presumption is that true, (although sinful) consent has been given and the marriage is presumed valid. This latter presumption considers that the right to the use was given but the fulfillment restricted. If the restriction is one of perpetual non-use (and not abuse), this is also against the substance of marriage if it implies that the conjugal right is not exchanged. However, such a condition of non-use is less clearly a vitiation of marital consent as is the condition of abuse. It is, moreover, not authoritatively determined nor generally agreed upon whether a condition of perpetual non-use or abstinence is in itself opposed to the substance of marriage. The condition may not be permitted, but a marriage so contracted must be presumed to be valid.