Taking the Pants from a Highlander

Most of the mathematical logicians who have come after Boole are men who would have stuck at the impossible subtraction in ordinary algebra.  They say virtually, "How can you throw into a heap the same things twice over; and how can you take from a heap things that are not there."  Their great principle is the impossibility of taking the pants from a Highlander.  Their only conception of the analytical processes of addition and subtraction is throwing into a heap and taking out of a heap.  It does not occur to them that the processes of algebra are ideal, and not subject to gross material restrictions.

From "Lectures on ten British mathematicians of the nineteenth century" by Alexander Macfarlane (1916).

(I should perhaps mention, for those mystified by the above reference, that Scotsmen, and presumably Highlanders in particular, are reputed not to wear any pants under their kilts.)