Estates in land are possessory interests in land.
These interests may be:
->Presently possessory (present estates), or
->They may become possessory in the future (future interests)
They also may be:
->Freeholds which give possession under some legal title or right to hold. Ex.: life estates
->Nonfreeholds which give mere possession. Ex.: leases
Additionally they may be:
->Potentially infinite duration, as in the case of fee simple.
->Limited duration, as in the case of an estate for years.
*Doctrine of merger: Whenever the same person acquires all of the existing interests in land, present and future, a merger occurs. That person then holds a fee simple absolute.
*Rule in Shelley's case: When the freehold estate (usually a life estate) is given to A, and in the same instrument a remainder was limited to the "heirs" or "heirs of the body", the purported remainder in the heirs is not recognized, and A takes both the freehold estate and the remainder. The rule converts what would otherwise have been a contingent remainder in the heirs into a remainder in the ancestor.(It is abolished in almost all states). Ex.: "To A for life, and then to the heirs of A". By virtue of the rule, A has a life estate, and a vested remainder in fee simple. (Here, the law of merger causes A's life estate to merge with his remainder so that A gets a present estate in fee simple)