Al-Kindi

The teaching

Taught from his own treatises, above all On First Philosophy, On the Intellect and On Dispelling Sorrows.

Truth from whatever source

Al-Kindi opens his First Philosophy with a rule for learners. We ought not to be ashamed to praise the truth and to take it from wherever it comes, even from peoples far from us and nations unlike us; for the seeker of truth nothing is worthier than the truth itself, and it never lowers the one who reaches for it. We owe thanks to those who brought us even a little of it, for they are partners in what we have gained, and each generation adds to what the last achieved. Philosophy is the knowledge of things in their reality, as far as a human being can know it, and its noblest part is first philosophy, the knowledge of the First Truth, which is the cause of every truth.

The world had a beginning

No body can be infinite in act. Take any finite part away from an infinite body: what remains is either finite, and then the whole, made of two finite parts, is finite; or it is infinite, and then a part is as great as the whole, which is absurd. Body, motion and time are never found apart, for there is no body without motion and no motion without time. So time too is finite, the world has a beginning, and it was brought into being from nothing by a cause outside it.

The True One

Everything we know is one in some way and many in another: a man is one man and many limbs, a number is one number and many units. Such unity is borrowed, and there must be a cause of unity in all things that is one in itself and in no way many: the True One. It is not matter or form, not quantity or quality or relation; it is not a genus, a species, a difference, a property or an accident; it is not motion, soul or intellect. Nothing can be said of it but what it is not. It is the cause of the being of all things, for to be is to be one, and the unity that flows from it keeps each thing in being; were it withdrawn, the thing would cease.

The four intellects

In On the Intellect he sets out four kinds. The first is the intellect that is always in act, the cause of all that is known. The second is in the soul only in potency, able to know but not yet knowing. The third has passed in the soul from potency to act and is held as a possession, which the soul uses when it wishes, as a writer uses his skill in writing. The fourth is the intellect that shows itself when the soul is actually thinking. The first brings the second into act, as fire makes cold wood hot, and so all human knowing is kindled from beyond the soul.

Dispelling sorrow

Sorrow, al-Kindi teaches, is a pain of the soul that comes from losing what one loves or failing to get what one seeks. Every thing of the senses can be lost, so whoever sets his heart on them must sorrow, and whoever wants a good that cannot be taken away must love the things of the mind, which no one can steal. Sorrow is not by nature; it comes from our judgement and our habit, and time wears it away by itself. Reason can do now what time does slowly. Consider that what was lost was a loan from the Lender of all, who may take it back when he wishes, and that to grieve at its return is to forget the thanks owed for the time it was lent.

He gives the parable of a ship. Travellers put in at an island, and some go ashore to gather flowers, shells and coloured stones. Those who come back quickly find the best places on board; those who linger find cramped corners; those who load themselves with things find no room, and must carry their burdens in discomfort; and some wander so far that the ship sails without them and they perish. The island is this world, the ship is the passage to our true home, and what is gathered here is to be held lightly.

The strings of the lute

His treatises on music teach that sound acts on the soul and the body because the whole world is ordered by the same numbers. The four strings of the lute answer to the four elements, the four humours and the four seasons: the highest string to fire and yellow bile, the second to air and blood, the third to water and phlegm, and the lowest to earth and black bile. Played in the right mode at the right time, each stirs the humour that belongs to it, gladdening, calming or rousing, and so music is a medicine for the soul. The house gives this as his account of music, not as a treatment.

Rays

On Rays, which survives only in Latin under his name, teaches that every thing in the world sends out rays in every direction, so that each thing acts on every other and the whole world is bound into one web. The heavens act on the elements by their rays, and the elements send rays too; so does a word spoken with intent and with a strong image in the mind, a figure drawn, an offering made. None of these, the treatise holds, acts by a power of its own, but by the harmony of the heavens that runs through all.

Reading a hidden message

His treatise on secret writing gives the method of breaking a cipher in which each letter is replaced by another. Take a plain text in the same language long enough to fill about a sheet, and count how often each letter occurs: call the commonest the first, the next the second, and so on. Then count the symbols of the cipher in the same way, set the commonest symbol for the commonest letter, the second for the second, and test each guess against the words it makes. Short messages mislead the count, so the longer the message, the surer the reading.