Robert Grosseteste Quotes

Vacuum stands and remains a mathematical space. A cube placed in a vacuum would not displace anything, as it would displace air or water in a space already containing those fluids.

The experimental universal is acquired by us, whose mind's eye is not purely spiritual, only through the help of the senses. For when the senses several times observe two singular occurrences, of which one is the cause of the other or is related to it in some other way, and they do not see the connection between them... And from this perception repeated again and again and stored in memory, and from the sensory knowledge from which the perception is built up, the functioning of the reasoning begins. The functioning reason therefore begins to wonder and to consider whether things really are as the sensible recollection says, and these two lead the reason to experiment... But when he has administered many times with the sure exclusion of all other things [that could be mistaken for the cause]... then there is formed in the reason this universal... and this is the way in which it comes from sensation to a universal experimental principle.

Ostensive demonstration is that which concludes directly to that which is in question. Reduction ad impossibile is that which, when something the opposite of that which is in question has been assumed, concludes with some other proposition directly to a known and manifest impossibility, from the opposite of which the investigator is led back to the original proposition in question. But there is a difference between ostensive demonstration and reduction ad impossibile, because the former proves from things prior in the order of nature but the latter from things posterior in the order of nature. When things prior in nature are better known in the intellect of the person making the demonstration the process is carried out ostensively; but when posterior things are better known to his intellect then the demonstration is carried out per impossibile... in demonstration carried out per impossibile the showing of the original thing in question is carried out by means of things posterior to it in the order of nature... And there is in the contrary, falsely supposed in predicate of subject, a connecting term by which something is implied to be which impossible in the nature of things.

Just as the light of the sun irradiates the organ of vision and things visible, enabling the former to see and the latter to be seen, so too the irradiation of a spiritual light brings the mind into relation with that which is intelligible.

I hold that the first form of a body is the first corporeal mover. But this is light, which as it multiplies itself and expands without the body of matter moving with it, makes its passage instantaneously through the transparent medium and is not motion but a state of change. But, indeed, when light is expanding itself in different directions it is incorporated with matter, if the body of matter extends with it, and it makes a rarefaction or augmentation of matter; for when light is itself charged with the body of matter, it produces condensation or rarefaction. So when light generates itself in one direction drawing matter with it, it produces local motion; and when light within matter is sent out and what is outside is sent in, it produces qualitative change. From this it is clear that corporeal motion is a multiplicative power of light, and this is a corporeal and natural appetite.

Power from natural agents may go by a short line, and then in its activity greater... But if by a straight line then its action is stronger and better, as Aristotle says in Book V of the Physics, because nature operates in the shortest way possible. But the straight line is the shortest of all, as he says in the same place.

In a vacuum which is imagined as infinite there cannot be local differences, both on account of its infinity, and also because of the fact that the vacuum, if it exists, would have no nature but a privation, and therefore it can have no natural differences.

The head is borne towards the heavens and has two lights, as it were the sun and moon.

That is better and more valuable which requires fewer, other circumstances being equal, just as that demonstration is better, other circumstances being equal, which necessitates the answering of a smaller number of questions for a perfect demonstration or requires a smaller number of suppositions and premises from which the demonstration proceeds. For if one thing were demonstrated from many and another thing from fewer equally known premisses, clearly that is better which is from fewer because it makes us know quickly, just as a universal demonstration is better than particular because it produces knowledge from fewer premises. Similarly in natural science, in moral science, and in metaphysics the best is that which needs no premisses and the better that which needs the fewer, other circumstances being equal.

The first corporeal form, which some call corporeity, I hold to be light. For light of its own nature diffuses itself in all directions, so that from a point of light a sphere of light of any size may be instantly generated, provided an opaque body does not get in the way. Corporeity is what necessarily follows the extension of matter in three dimensions, since each of these, that is corporeity and matter, is a substance simple in itself and lacking all dimensions. But simple form in itself and in dimension lacking matter and dimension, it was impossible for it to become extended in every direction except by multiplying itself and suddenly diffusing itself in every direction and in its diffusion extending matter; since it is not possible for form to do without matter because it is not separable, nor can matter itself be purged of form. And, in fact, it is light, I suggest, of which this operation is part of the nature, namely, to multiply itself and instantaneously diffuse itself in every direction. Therefore, whatever it is that produces this operation is either light itself or something that produces this operation in so far as it participates in light, which produces it by its own nature. Corporeity is therefore either this light, or is what produces the operation in question and produces dimensions in matter in so far as it participates in this light itself and acts by virtue of this same light. But for the first form to produce dimensions in matter by virtue of a subsequent form is impossible. Therefore light is not the form succeeding this corporeity, but is this corporeity itself.

The diligent investigator of natural phenomena can give the causes of all natural effects... by the rules and roots and foundations given from the power of geometry.

The space of the real physical world must be considered full, that is a plenum, because a vacuum could have no physical existence.

And since the proportions of the human voice and the gesticulations of the human body are regulated by the same modulation as that by which sound and the motion of other bodies are, musical thought is subalternated not only to the harmony of human voice and gesticulation, but also of instruments and of those whose delectation consist in motion or sound and with these the harmony of the celestial and non-celestial. And since the concordance of times and the composition and harmony of the lower world and of all things composed of four elements come from celestial motions, and, moreover, since it is necessary to find the harmony of causes in their effects, the study of music also extends to knowing the proportions of times and the constitution of the elements of the lower world, and even the composition of all the elements.

This part of optics, when well understood, shows us how we may make things a very long distance off appear as if placed very close, and large near things appear very small, and how we may make small things placed at a distance appear any size we want, so that it may be possible for us to read the smallest letters at incredible distances, or to count sand, or seed, or any sort of minute objects.

One cause, in so far as it is one, is productive of only one effect. I do not rule out several efficient causes of which one is nearer and another more remote in the same order. Thus when I say simply 'animal', I do not exclude another substance or particular substance. Hence motion, in so far as it is one, is productive of only one effect. But motion is present in every body from an intrinsic principle which is called natural. Therefore an efficient cause simply proportional to the motion is present in all bodies. But nothing is present in common in every body except primitive matter and primitive form and magnitude, which necessarily follows from these two, and whatever is entailed by magnitude as such, as position and shape. But simply through magnitude a body does not receive motion, as is clear enough when Aristotle shows that everything that moves is divisible, not, therefore, simply because of magnitude or something entailed by magnitude is a body productive of motion. Nor is primitive matter productive of motion, because it is itself passive. It is therefore necessary that motion follow simply from the primitive form as from an efficient cause.