For Bacon, spirit in general is a “breath compounded of an airy and a flamy substance” (OFB VI 321). One extreme is that of the air (rather cold and inactive), the other that of fire. But the mixture of air and fire is not mechanical (OFB XII 355); it is a complete mixture (which cannot be simply evaluated in terms of more air/less fire; or more fire/less air, but has a ‘mysterious’ character, OFB XII 352, 376 etc.). In between ‘air’ and ‘fire,’ we have a whole range of spirits: the non-living ones “are nearly consubstantial to air,” while the “vital spirits come closer to the substance of fire.”(OFB XII 354-5) One fundamental principle in Bacon’ natural philosophy is that there is no tangible body devoid of spirit. By contrast, spirits can be ‘free’ or ‘enclosed’ in matter. Meanwhile, spirits also come in all sorts of shapes and forms: and although Bacon sometimes attempted classifications of pneumaticals (i.e. according to their rarity in HDR) it is clear that their diversity resist any form of unique classification.

In the late natural histories, one can find series of experiments which seem to attempt to classify pneumaticals according to their properties. In some cases, the classification takes into consideration observational properties of pneumatics (hence, the resulting ‘classification’ will be called ‘phenomenological’). In some other cases, (esp. Sylva) the principle of classification seem to be the prevailing process (i.e. physical classifications). There is arguably also an attempt to divide spirits and matter in metaphysical terms.

It is not only that these classifications are not unique, they are also overlapping. However, the recurrence of such attempts to classify spirits in the late natural history seem to signify that Bacon was persuaded of the importance of achieving some form of classification, or typology of pneumatic substance.

Meanwhile, Sylva constantly insists on the diversity of spirits and the diversity of properties characterizing spirits. Spirits are “nothing else but a natural body, rarefied to a proportion, and included in tangible parts of bodies;” in addition, they are many differences between spirits: “they be no less differing one from the other than the dense or tangible parts.”(SEH II 381)

Phenomenological classifications

1. Classification of spirits according to their rarity (HDR)
2. Classification of spirits according to their heat (sources of heat, how the heat is processed…) (OFB XII 359)

Close distillation (forcing matter/spirit to react to heat in a close container) (SS I 99), and other experiments with closed containers destined to mix air and flame or watery and oily

3. Classification of spirits according to the qualities of the mixture of air and flamy (which gives it empirical characteristics such as “greediness,” “lassitude” …).

Physical classifications

1. Classification according to the organization of spirit in matter (branched, cells, cut-off)
2. Classification according to the even/uneven distribution of spirit in matter and the fineness of the spirit AND/OR strenght[1]
3. Classification according to the processes that gets activated

Spirits are said to be the causes of all processes (SS I 98) (but whether a process or another takes over is also a property of spiritual substance?)

Classification in terms of activity (resulting from the activated appetites)

[1] Spirits “weak” “clinging loosely, … practically consubstantial with plain air,” “dwelling mainly the outer parts of the body.;” “transient guests” in bodies – Versus spirits “stronger,” “further inside,” “submerged and buried deeper in the solid parts of the thin.” (OFB VI 291) Also, there is a rule in HVM which links the even/non-even distribution of the spirit with its properties/activity – abundance of spirit non-evenly distributed makes the spirit more predatory OFB XII 361.

Metaphysical classification (?)

Spiritus vitalis/Spiritus mortualis (HVM, OFB XII 351)

(Also: (DVM OFB VI 352-3) – vital spirit, peculiar to living things OFB VI 357 – differs from the other spirits not only because it is differently organized, but because it has an inner warmth and because it feeds upon “the moist parts and joice of the living body” (OFB VI 359))

HVM: Rule/Canon IV: In all living things there are two kinds of spirits: non-living ones (Mortuales) of the kind found in inanimate substances, and the superadded vital spirits.

Vital spirit is something different from all the spirits that exist in inanimate bodies because: it needs aliment, it is somehow closely connected with the body (being ‘in charge’ of the body and all the other spirits), it ‘rules’ the other spirits and the body.

Thus we should know that there exist in flesh, bones, membranes, organs, and every single part of the human body, spirits which pervade them while they live, and which are identical to those which exist in those parts – flesh, bone, membrane and the rest – when they are separate and dead, and identical to the ones remaining in the corpse. But the vital spirit, though it rules and has some consent with them, is very different from them, as it is integral and self-consistent [integralis, & per se Constans]. Now the non-living and vital spirits differ in two main ways: the first is that the non-living spirits are not in the least self-continuous, but are as it were cut off and surrounded by the grosser body which intercepts them rather as air is intermixed in snow or froth. But all vital spirit is self-continuous through certain channels which it pervade, without being completely intercepted. This spirit too is of two kinds: the one is just branched and runs through little thead-like tubes [Ducturs, & tanquam Lineas]’ the other has in addition a cell [Cellam] so that it is not just self-continous but is also gathered together in some hollow space and, relative to the body, in an appreciable quantity; and in this cell is the source of the rivulets which go their separate ways from there. This cell is mainly in the cerebral ventricles, which in humbler creatures are narrow, such that the spirits seem to be diffused through the whole body rather than concentrated in cells, as we see in snakes, eels, and flies whose individual parts still move after being cut away. (OFB XII 351-353)

Although Bacon attempts to reduce this fundamental difference to physical and phenomenological differences, it is not entirely clear that this is a successful enterprise (or an enterprise that can succeed). In principle, the differences are:

• Of organization (non-living spirits are cut off and not organized) and distribution (within the body; how well distributed are the vein, how far away from the cells etc. see DVM)
• Of composition (all spirits are a mixture of air and flame, and the living one are closer to the nature of flame, but Bacon emphasizes that this is not a mechanical mixture and hence “when this rule states that vital spirits come closed to the substance of flame, it must be taken to mean that they do so more than the non-living ones, and not that they are more flamy than airy” (OFB XII 355).
• Of behavior/appetites (the non-living spirits have two appetites/desires – to multiply, and to fly and meet with connaturals; living spirits have more appetites, for example they are “absolutely terrified of leaving its body” – which means that living spirits are “principal” spirits of bodies and they are metaphysically united with their bodies)
• Of heat/warmth (OFB VI 357)

Another major difference is said that non-living bodies/spirit do not need aliment, while the others do (but, however, spirits in inanimate bodies ‘eat-up’ matter)

DVM: But it is unquestionably the case that among the difference of the spirit there are two in particular which have the greatest importance: for spirits differ in body or in force, for we find that some are more biting, lively and robust while others are duller and weaker. And that very force proceeds either from the nature of the thing, or from the length of time that has elapsed since the death of the body. Alternatively, spirits vary in fraction or comminution, for we find bodies in which the spirtis are more diffused and dispersed so that the portion of spirit in any given part is less than it might be, but other bodies in which the spirts have more space and larger concentrations. But again, we find that the distribution of spirits with reference to their sites is more uniform in certain bodies so that the spirits are diffused more evenly in particular parts of the body; but in other bodies they are distributed less evenly so that the residences of the spirit are more spacious in one place and more confined and circumscribed in another. (OFB VI 282-3)

Hypothesis 1: As with many of his new concepts, Bacon seems to use “spirits” in more than one way; using a range of traditional, loose meanings (spirits are the breath of life, they are the source of activity in the Universe and they originate “in the stars,” there are living spirits and non-living spirits etc.) and a more specific, technical meaning (a class of material substances characterized by rarity, heat (potential or actual heat), active powers, the capacity to diffuse at considerable distances, and other several properties such as greed which Bacon attempts to express in terms of combinations of attributes).

Hypothesis 2: There are small but significant differences between DVM and HVM on the one side and SS on the other regarding the fundamental and derivative properties of pneumaticals. These differences can originate in the fact that in SS Bacon asks different questions and is interested in different aspects of the workings of spirits than in the other two works. Thus, there is no equivalent of spiritus mortualis at work. Meanwhile, there seem to be a distinction between the principal spirit of a body and other spirits which might (or might not) inhabit the same body. The principal spirit can be the living spirit of DVM and HDR. Meanwhile, there clearly are other organized spirits at work in the same body (a scion grafted on a stock poses this problem of two principal spirits ‘fighting’ and one is overcoming the other).

Sylva Sylvarum has a number of experiments which seem to be saying that there is no metaphysical distinction between vital spirits and the others, that there is indeed a merely variation in the mixture of air and flame at work, and that one can simply vary the proportion of the two in the mixture

SS1.30 “although air and flame being free will not well mingle; yet bout in by a body that hath some fixing, they will. For that you may best see in those two bodies (which are their aliments) water and oil; for they likewise will not well mingle of themselves, but in the bodies of plants and living creatures they will.”