OBSERVANCE OF PREROGATIVE-PEREMPTORY ON THE FATHER
The above-mentioned underlying biblical injunction precludes the father from depriving the firstborn of his particular right of inheritance. Consequently, any form of testamentary disposition (see *Wills) by a father purporting to bequeath to the firstborn less than his prescribed double portion of the inheritance is null and void. This rule only applies, however, where the father has clearly adopted the language of a testator, since a father cannot change the laws of inheritance as such (Maim., Yad, Naḥalot 6:1). Consequently, if the father has expressed himself in terms of making a gift, his disposition will stand (although "the spirit of the sages takes no delight therein," BB 133b and see Posekim), since he may freely dispose of his assets by way of gift. Since the exercise of the birthright involves a corresponding greater liability for the debts of the estate, the firstborn may escape such additional liability by way of renouncing his prerogative before the division of the estate (BB 124a; Sh. Ar., ḤM 278:10).