Under a strict Scottish entail, made prior to 1848, the tenant in possession had never more than a life estate only, and consequently could not bar the entail. He may now do so with the consent of one or more of those in remainder. If born after 1848, or after the execution of any entail made subsequently, he may bar it without any consent. To make an entail effectual, it must have contained clauses prohibitory against the possessor selling, encumbering, or anew limiting the estate, irritant (avoiding) of any such acts, if he should do them, and resolutive (forfeiting) of his right to the estate in that case. These three sets of clauses constituted the fetters of a strict entail. Defect in any one avoided the entail as regards the particular procedure, whether selling, encumbering, or devising ; but now it avoids the entail in all respects.

Source: Kinnear, Digest of House of Lords cases (1865), pg. 354.