Accession generally refers to the addition of something to personal property through the addition of labor. Accession is derived from the civil law notion that a person has a right to not only their property, but also to that which the property produces, either through natural or artificial means. Accession may happen in three ways: (1) naturally; (2) artificially; (3) from the combined operation of nature and industry.
- Natural - The increase of an animal, the yield of fields, the rent of a house, etc., belong to the owner of the animal fields, and house, respectively. Thus, the offspring of a female animal is the property of her owner, even it is the result of intercourse with a male belonging to someone else.
- Artificial - If the owner of a piece of leather can prove that it has been altered to be turned into a pair of shoes, then under common law, that owner would retain title to such shoes.
- Mixed - An example of the third kind of accession is the building of a house on another's ground, or the planting of trees or sowing of vegetables in another s field. The house, trees, etc., belong to the master of the soil after making suitable compensation to the builder, planter, etc.