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For someone living in two dimensions and becoming aware of three, it might be easier to think of four than for someone living in three dimensions.
The cherished feeling of oneness might be misleading …
That Point is a Being like ourselves, but confined to the non-dimensional Gulf. He is himself his own World, his own Universe; of any other than himself he can form no conception; he knows not Length, nor Breadth, nor Height, for he has had no experience of them; he has no cognizance even of the number Two; nor has he a thought of Plurality; for he is himself his One and All, being really Nothing. Yet mark his perfect self-contentment, and hence learn this lesson, that to be self-contended is to be vile and ignorant, and that to aspire is better than to be blindly and impotently happy. (ch. 20)