This paper examines the metaphysical question of 'ensoulment' in relation to the theory, put forward in an earlier paper, that human life begins when the newly formed body organs and systems of the embryo begin to function as an organised whole, at which stage there is evidence of a change of nature. Although Roman Catholic theology teaches that a human being is a union of physical body and spiritual soul, it is incorrect to interpret this in a dualistic sense. The (...) meaning of 'soul' is considered and the conclusion reached that although both in the religious context and apart from it abortion is difficult to justify at any stage after conception, it does not follow that the use of 'spare' In Vitro Fertilisation (IVF) embryos should be rejected. If 'ensoulment' does not occur until the new organism functions as a whole then a decision not to make use of IVF embryos for medical purposes would be a heavy responsibility and not a 'safe' way out. (shrink)