27 These parts of the law, however, have not been left without due alteration, a constitution having been inserted in our Code by which we have in these respects amended the rules relating to legacies and fiduciary bequests no less than to inheritances, as will be made clear by a perusal of the enactment, which, however, still maintains the old rule that an uncertain person cannot be appointed guardian: for when a testator is appointing a guardian for his issue, he ought to be quite clear as to the person and character of the party he selects. 28 An afterborn stranger could and still can be instituted heir, unless conceived of a woman who cannot by law be a man's wife. 29 If a testator makes a mistake in any of the names of the legatee, the legacy is nevertheless valid provided there is no doubt as to the person he intended, and the same rule is very properly observed as to heirs as well as legatees; for names are used only to distinguish persons, and if the person can be ascertained in other ways a mistake in the name is immaterial. 30 Closely akin to this rule is another, namely, that an erroneous description of the thing bequeathed does not invalidate the bequest; for instance, if a testator says, 'I give and bequeath Stichus my born slave,' the legacy is good, if it quite clear who is meant by Stichus, even though it turn out that he was not born the testator's slave, but was purchased by him. Similarly, if he describe Stichus as 'the slave I bought from Seius,' whereas in fact he bought him from some one else, the legacy is good, if it is clear what slave he intended to give. 31 Still less is a legacy invalidated from a wrong motive being assigned by the testator for giving it: if, for instance, he says, 'I give and bequeath Stichus to Titius, because he looked after my affairs while I was away,' or 'because I was acquitted on a capital charge through his undertaking my defence,' the legacy is still good, although in point of fact Titius never did look after the testator's affairs, or never did, through his advocacy, procure his acquittal. But the law is different if the testator expresses his motive in the guise of a condition, as: 'I give and bequeath such and such land to Titius, if he has looked after my affairs.' 32 It is questioned whether a legacy to a slave of the heir is valid. It is clear that such a legacy is void if given unconditionally, even though the slave ceases to belong to the heir during the testator's lifetime: for a legacy which would be void if the testator died immediately after making his will ought not to become valid by the simple fact of the testator's living longer. Such a legacy, however, is good if given subject to a condition, the question then being, whether at the vesting of the legacy the slave has ceased to belong to the heir.