Aren’t there too many unknowns even in our knowns to make the search frustrating? If we can think of the knowable unknown—not resting in the domain of metaphysics—then there could be a possibility of developing instrumentation for its investigation or study. But can reason posit anything about this kind of “knowable unknown” to pursue our inquiry in order to open out new lines of exploration. I wonder. Of course it is futile to talk about unknowable of any kind—known or unknown. If we have to extend the list of tools given in the Synthesis-passage we should also include in it the Mind-sense, Manas, used by reason. And then to quote a passage from the Letters: “Science itself has come to the conclusion that it cannot, as it once hoped, determine what is the truth of the things or their real nature, or what is behind physical phenomena; it can only deal with the process of physical things and how they come about or on what lines men can deal with and make use of them.” Though written some 70 years ago, it is valid even today. And about Manas: “Manas, say our philosophers, is the sixth sense. But we may even say that it is the only sense and that the others, vision, hearing, touch, smell, taste are merely specialisations of the sense-mind which, although it normally uses the sense-organs for the basis of its experience, yet exceeds them and is capable of a direct experience proper to its own inherent action.”