  With quaternion theory we see that, in the final analysis, Bacon was not a mechanist philosopher. His theory of matter underwent an important transformation, moving in the direction of ‘forms’, which we would nowadays subsume under biology or the life sciences rather than under physics. Bacon distinguishes between non-spiritual matter and spiritual matter. The latter, also called ‘subtle matter’ or ‘spirit’, is more reminiscent of Leibniz' ‘monads’ than of mechanically defined and materially, as well as spatially, determined atoms. The spirits are seen as active agents of phenomena; they are endowed with ‘appetition’ and ‘perception’ (Bacon I [1889], 320–21: Historia Vitae et Mortis; see also V, 63: Sylva Sylvarum, Century IX: “It is certain that all bodies whatsoever, though they have no sense, yet they have perception: for when one body is applied to another, there is a kind of election to embrace that which is agreeable, and to exclude or expel that which is ingrate”).