Life and Paradigm
You must have a paradigmatic basis of understanding the human body and healing/sickness in order to use Life. This paradigmatic understanding will then be assigned to a particular Ability on your sheet. For example, someone with a more surgical basis of understanding may assign Medicine as their means of navigating the Life sphere, whereas a faith healer may instead attribute Occult to their understanding, a Herbalist may decide to go with Science as a reflection of chemistry in herbalism, an Etherite may decide to go with Technology or Science.