We may perhaps illustrate this conception of a knowledge which, though imperfect, is yet final, by an instance borrowed from elementary Mathematics. We know absolutely and precisely, _e. g._, what the symbol π stands for. π is completely determined for us by the definition that it is the ratio of the circumference of a circle to its diameter. And again, we can define unequivocally both the terms, circumference and diameter of the circle, which we have employed in our definition of π. Thus our knowledge of the meaning of the symbol is clearly final; no fresh accretion to our knowledge will make any modification in it. At the same time, our knowledge of π, though final, is imperfect. For the quantity π is incommensurable, and thus we can never precisely evaluate it. All we can do is to assign its value correctly within any desired degree of approximation. Again, while no approximation gives an absolutely correct value for the quantity, one approximation is, of course, closer than another. Because no approximation is more than approximately the truth, it by no means follows that all are equally wide of the mark. Similarly, it may well be that, though we can say with finality what the general nature of experience and experienced Reality as a systematic whole is, yet, when we come to ask after the character of the system in detail, we have to depend on sciences which are merely approximate in their results; it will not follow, as is sometimes assumed, that the categories of one science do not present us with a nearer approximation to the absolute truth than those of another.[25]