This, in fact, cannot be done. While life may be present in the absence of viability, viability cannot exist much less be achieved in the absence of life, or vitality. Viability is a condition and a property of vitality. One cannot posses or achieve viability in the absence of vitality. Potential is meaningless in the absence of a potentiator.
Viability is, at best, an indicator of the disposition of life rather than the determinate of life.
However, this did not deter Blackmun. The ability of the pre-partum fetus to grow and develop within the womb qualifies it, by definition, as viable and therefore vital or alive. The notion that viability can be achieved in the absence of vitality is an unsupportable assumption. Blackmun failed to understand that the presence of viability always indicates the presence of life, but the presence of life does not necessarily indicate viability. Stated another way, the absence of viability does not necessarily indicate the absence of life.