Even if property was agreed by the parties to be the separate property of a particular party, or is separate property because of a rule of law, in some States, if such property was commingled into the marriage, it can be considered converted to marital property. This often happens when a other spouse engages in acts that creates appreciation in the separate property. This can take place for instance when one spouse owns a house and the other spouse spends time working on the house to repair it and those acts create an increase in the value of the house. At the very least, the non-owner spouse can argue that the appreciation in value has become part of the marital property and should be divided in a divorce.
separate property is not usually divided in divorce proceedings