Missing a soul that endows bodies with life: an introduction

In the history of ideas, innumerable attempts to explain life and to define living activities have invoked the notion of the soul. Yet this theoretical entity seems to be an unfathomable thing. Difficulties beset the mere definition of it, and controversies span from whether the soul is a material body or an immaterial form, an immortal or a mortal thing, a subject of experiential or of theoretical knowledge, to the question of whether it is the subject of a specific discipline or rather of a scientia de anima that, in the Aristotelian tradition, was also regarded as a part of natural philosophy—the field of philosophy that deals with natural particulars. Not only was the soul thought, from a theological angle, to define the unity and unicity of living beings (and in some cases, even their individuality), but it was also seen as the source of several bodily activities such as nutrition and growth in living beings. And since some of the beings that grow and nourish themselves also sense and think, the relation of the origin of vegetative powers to the origin of perceptual and intellectual powers has always been an object of debate. In this sense, the soul has not just been a topic of one specific field, but has rather drawn upon many disciplines, combining the work of philosophers, religious thinkers, physicians, naturalists, chymists, and so on, thereby blurring the boundaries between different fields of knowledge. Botanical treatises of the Renaissance, for example, begin with the definition of the soul of plants and its primary role in bringing forth vegetal activities. Indeed, the presence of the soul was thought to be involved also in the life of animals, human beings, and, in some cases, it was even ascribed to minerals and stones, not to speak of the world-soul, the latent idea that the entire cosmos is animated with a soul. Furthermore, the theory of the materiality of the soul was developed since Antiquity and found new momentum in early modern times, in the reappraisal of Epicurean ideas by thinkers such as Guillaume Lamy, Pierre Gassendi, and Julian Offray de La Mettrie. Yet, with the Cartesian Henricus Regius, the understanding of vegetative, sensitive, and rational souls as material importantly surfaces as a peculiar attempt to mechanize the living functions of bodies