But just as those three worlds are not thought of as separate in time, so they are not separate in space. They are not like the seven heavens and seven earths of Muslim literalists, which stand, story-fashion, one above the other. Rather they are, as expressed above, modes of existence, and might be compared to the speculations on another life in space of n dimensions, framed, from a very different starting-point and on a basis of pure physics, by Balfour Stewart and Tait in their “Unseen Universe.” On another side they stand in close kinship to the Platonic world of ideas, whether through neo-Platonism or more immediately. Sufiism at its best, and when stripped of the trappings of Muslim tradition and Qur’anic exegesis, has no reason to shrink from the investigation either of the physicist or of the metaphysician. And so it is not strange to find that all Muslim thinkers have been tinged with mysticism to a greater or less degree, though they may not all have embraced formal Sufiism and accepted its vocabulary and system. This is true of al-Farabi, who was avowedly a Sufi; true also of Ibn Sina, who, though nominally an Aristotelian, was essentially a neo-Platonist, and admitted the possibility of intercourse with superior beings and with the Active Intellect, of miracles and revelations; true even of Ibn Rushd, who does not venture to deny the immediate knowledge of the Sufi saints, but only argues that experience of it is not sufficiently general to be made a basis for theological science. In ethics, as we have already seen, the position of al-Ghazzali is a simple one. All our laws and theories upon the subject, the analysis of the qualities of the mind, good and bad, the tracing of hidden defects to their causes—all these things we owe to the saints of God to whom God Himself has revealed them. Of these there have been many at all times and in all countries, and without them and their labors and the light which God has vouchsafed to them, we could never know ourselves. Here, as everywhere, comes out al-Ghazzali’s fundamental position that the ultimate source of all knowledge is revelation from God. It may be major revelation, through accredited prophets who come forward as teachers, divinely sent and supported by miracles and by the evident truth of their message appealing to the human heart, or it may be minor revelation—subsidiary and explanatory—through the vast body of saints of different grades, to whom God has granted immediate knowledge of Himself. Where the saints leave off, the prophets begin; and, apart from such teaching, man, even in physical science, would be groping in the dark. [Sidenote: AGNOSTIC ATTITUDE]