Among Sufis there is a spiritual culture, a culture which recognizes four centers, each center being a vacuum, or a capacity, for pure intelligence to function in. This shows that man has the greatest possibility of knowing all that is knowable, and he has an even greater capacity than that: to realize all that can be known. If he only knew how he could achieve it! But, one may say, why must substance coming from vacuum learn to know, when vacuum is already the all-knowing state? The all-knowing state is not the same as a limited knowing state. To look at all is one thing, and to look at a flower with a little instrument is another thing. The conductor of an orchestra may hear the whole orchestra at the same time, and yet he may want to hear one instrument alone to know in how far it is correct.