A will being ambulatory is always revocable, unless in one or two exceptional instances. Undue influence is a ground upon which frequent attempts are made to set aside wills. Its nature is well explained in a judgment of Lord Penzance's: "Pressure of whatever character, whether acting on the fears or the hopes, if so exerted as to overpower the volition without convincing the judgment, is a species of restraint under which no valid will can be made." There is nothing corresponding to the querela inofficiosi testamenti, but unnatural provisions may be evidence of mental defect. The circumstances appearing on the face of the will which make it open to objection may either avoid it altogether or create a partial intestacy, the will remaining good as a whole. Where the will is not duly executed, e.g. if it is a forgery or if it is not signed by the testator or the proper number of witnesses, the will is not admitted to probate at all. Where it contains devises or bequests bad in law, as in general restraint of marriage, or tending to create perpetuities, or contrary to public policy, or to some particular enactment, only the illegal part is void. A remarkable instance is a well-known case in which a condition subsequent in a devise was held void as against public policy, being a gift over of the estate devised in case the first devisee, the eldest son of an earl, did not before his death obtain the lapsed title of Duke of Bridgewater. At common law there could be no larceny of a will of lands. But by the Larceny Act 1861 stealing, injuring or concealing a will, whether of real or personal estate, was punishable with penal servitude for life. Forgery of a will (at one time a capital crime) rendered the offender liable to the same penalty. Fraudulent concealment of a will material to the title by a vendor or mortgagor of land or chattels is, by the Law of Property Amendment Act 1859, a misdemeanour punishable by fine or imprisonment or both. History of wills in other jurisdictions United States In the 21st century, eighteen is the typical age of testamentary capacity. Full liberty of disposition is not universal. In particular, many states normally grant spouses the right to at least half the estate regardless of what the will says (or if no will can be