estates. One which takes effect in derogation of some other estate, and is either limited by the deed creating it, or authorized to be created by some person named in it. This is sometimes called a secondary use. 2. The following is an example: If an estate be limited to A and his heirs, with a proviso that if B pay to A one hundred dollars by a time named, the use to A shall ease, and the estate go to B in fee; the estate is vested in A subject to the shifting or secondary use in fee in B. Again, if the proviso be that C may revoke the use to A, and limit it to B, then A is seised in fee, with a power in C of revocation and limitation of a new use. These shifting uses must be confined within proper limits, so as not to create a perpetuity.