An estate upon limitation differs from an estate upon conditions subsequent in three respects; (1) No causa qua supra. And the lessor not his heirs cannot enter; for if the lessor might enter, then he ought to be in his former state, etc. and this might not be, because he hath aliened from him the reversion.' "Here Littleton reciteth one of the maxims of the common law; and the reason hereof, is, for avoiding of maintenance, suppression of right, and stirring up of suits; and therefore nothing in action, entry, or reentry, can be granted over; for so, under colour thereof, pretended titles might be granted to great men, whereby right might be trodden down, and the weak oppressed, which the common law forbiddeth, as men to grant before they be in possession." Coke Vol. II, p. 84-85 See Chapter IV (Who May Locate Claim. Section 13. In General) on Remainder.

entry is required in order to work a forfeiture of an estate upon limitation upon the happening of the event which marks its termination; (2) There may be a remainder after an estate upon limitation but not after an estate upon condition subsequent. The reason for this is that in the case of a remainder after an estate upon limitation the remainder is not considered to vest in derogation of the preceding estate. (3) If the condition in the case of the condition subsequent is the happening of an illegal act, or an act which is considered against public policy, the condition is void and the estate becomes absolute. In the case of an estate upon limitation, the restriction on the continuation of the estate is not disregarded because it is against public policy or involves an illegal act. Thus in a grant to A for life on condition that he shall not marry, the condition will be disregarded, as being against public policy, and A will take an absolute life estate; while a grant to A "as long as he remains single" is good and A's marriage would mark the termination of the estate.