Giordano Bruno argues in the book ‘De la Magia’ that the absolute vacuum does not exist, there is no space not occupied by any form of matter: In any space, empty as it may seem, there are bodies moving and passing but the invisible air particles, which are also matter.
The objects of the world are not isolated from each other, among them there is a continuum of matter, he states; imperceptible space among perceptible bodies is a continuum, rather than separate, mediates between them, communicates and keeps them united. The air (or 'aerial or ethereal spirit' as Bruno calls) is an imperceptible body, in principle, to our senses but by itself is a true physical intermediary continuous among all bodies, which is endowed with great activity and effectiveness upon the soul, that is closely united to it, he says, and has a strong resemblance to it, at a time that is very different from substance of thicker perceptible objects that it links.
"The vacuum, i.e. a space without bodies, does not exist: A body does not leave a space with no being replaced by another. Certainly the soul leaves the body it occupied in life, but cannot leave the universal body -unless we prefer to say that it cannot be abandoned by the universal body-. It is therefore inextricably linked to the universal matter, so as its particular nature is full and continuous everywhere, it recognizes everywhere the corporeal matter which coexists with it. It is followed, he concludes that the vacuum is not a disembodied space, but a space in which several bodies succeed and move, hence the continuous movement of body parts towards other body parts, through a continuous space not interrupted, as if the vacuum was merely a mediator between two full -except want to call vacuum to space in which there is no perceptible body-.
An imperceptible body is a truly continuous body -etheric air or spirit-; it is endowed with a huge activity and a huge efficiency, while is closely united to the soul, because of their similarity; because it is away over the rudeness of coarser perceptible substance of the compounds. The invisible and spiritual bodies -those from which comes virtue present in the sensitive bodies- are endowed with the aforementioned effectiveness, this is what it shows the aerial spirit that makes flux and reflux the whole sea, and the indomitable push of winds that, even with clear and calm weather, devastate the land, destroy the trees, stoop the ships. As pointed Lucretius so well, that spiritual body is the one who performs all operations in sensible bodies: in turn most philosophers thought that it was no different from the soul, from which the formula of the poet to describe the air, 'quantum ignes animaeque valent', 'all fires and winds can' (Virgil, Aeneid, VIII, v 403). As regards the fire, oblivious to the gross matter of coals that are burning bodies merely, it is understood that it only differs from the air by accident. The real fire is a real spirit, inside a body in combustion, as being contained, asleep; outside that body, it exists full-fledged, full of vivacity; and it is in an intermediate state in the flame, as set in motion." (De la Magia, p. 29-30)
The air is a physical and spiritual body at once: is the wind that pushes and moves liquids and solids, and that feeds the fire, and that the flame shows its movement, and acting on the sensitive bodies is thus invisible matter of soul. Soul and spirit, according to an ancient tradition in philosophy that Bruno gathers, are air, a very fine and subtle air.
"From water to steam, from steam to air, from air to the finest and sharpest etheric body, is produced the mutation of the same substance and matter to which the Egyptians, Moses and Diogenes of Apollonia called 'spirit'. There is divergence in the fact that Moses does not distinguish the soul of the spirit (if one adheres to his writings, without prejudging the meaning) while the others have made a difference." (p. 31)
The sight of Bruno is panpsychism: the universe has soul. Air is a spirit that touches and unites everything. Air is an invaluable stuff, apparently, to our senses but actually acts on our soul: air is spirit therefore, also in the metaphysical sense. It is what unites and connects physically all, while it is 'the soul of the universe' acting on our personal soul, our thinking and our intelligence; it is 'the first intelligence': it is God himself, according to Bruno.
"Some spirits inhabit human bodies, some inhabit the bodies of other living beings, plants, stones, minerals; in short there is nothing deprived of spirit, of intelligence; matter fleets from a spirit to another, from a nature or composition to another, and the spirit fleets from one matter to another; there is alteration, mutation, passion and finally corruption, i.e. separation of certain parts and composition with others. Death is nothing but dissolution." (p. 42)
"All spiritual substance is reduced to one; every spiritual substance is reduced to a triad. The soul, God and the first intelligence above all things, the soul of the universe" (p. 44)
Our soul is fed by the soul of the universe, while the body is fed by air; the air gives them life. And our intelligence, which is what makes us able to relate things, at once is a reflection of this universal intelligence that relates them all. Intelligence, thought, passions, instincts... the manifestations of our soul or psyche, are in the air. It is in this context that Bruno speaks of God and spirits in general and of ‘demons’ when spirits produce some manifestations of negative character in the soul (psyche) of people.
To him the phenomena of the human soul has a physical existence outside our body; he equates these demons to household or 'pareterals' Roman gods, others had a specific name and certain power recognized in some places, and more noble others had a relationship with music, hymns and musical instruments according to ancient mythology, gods all of them foreign to the thinking of the monotheistic religions, and inferior to God. (Other authors don't speak of 'demons' but of spirits in general, or 'angels', as Eckhart, in the Christian tradition, but ultimately the treatment given to these 'minor spirits' is almost the same as Bruno.) There are spirits physically in the air ('angels' or 'demons') organized by type of instincts, passions and thoughts that they arise in us.
"The proof that demons are of corporeal nature, as diverse and varied as diverse and varied are all body types, is experiencing affections, desires, movements of anger, jealousy, identical to those felt by people and beings made of thicker and sensitive matter." (p. 45)
"Above the condition of those demons stands the God one which, by nature, 'has no need of us, is not sensitive to the favors nor is touched by anger'." He said using the words of Lucretius (De Rerum Natura, II, V, 650-651). (p. 46)
"It must be said with confidence and kept on thinking that all things are full of spirit, soul, upper power, God or divinity, and that intellect and soul are all integral parts but not all do everything in everywhere. This is what the poet (Virgilio) refers inspired by the Pythagorean doctrine (and plays the Aeneid, VI, V, 724-729).
'And above all, sky and lands, liquid plains,
The bright globe of the moon, and the Titanic star,
An inner blow nurtures them; infused to all limbs,
The spirit moves throughout its mass, and mixes in the great body.
Men and animals, birds, all extract life from there,
And these monsters the waves carry under its marble surface.'
This is also the sense that everyone attributes to the sacred arcana, as in Psalm and the Book of Wisdom: "The spirit of the Lord has filled the world, and what contains all things', and moreover 'I fill heaven and earth'.
Corporeal substance is distinguished from such substance of thought, soul, sublime spirit in this: the corporeal whole is all in the entire universe, while the other substance is all entire anywhere, constituting a sort of anything and restoring the image of the whole, here more vividly, more darkly there, here about the unique way, multiple ways there... If all the blows ['spiritus'] and parts of the air they will join thus in a single ocean, they will form a unique soul, for many they were. The philosophers conclude from this that there is single matter, a single spirit, a single light, a single soul, a single intellect." (p. 46-47)
Bruno, Giordano. De la Magia. De los Vínculos en General. Cactus, Buenos Aires, 2007.