Ten times in those ten minutes he was on the point of jumping up, but Donal found a word sufficient to restrain him.

When the ten minutes were over, he set him an addition sum.

The boy protested he knew all the rules of arithmetic.
"But," said Donal, "I must know that you know them; that is my business.

Do this one, however easy it is." The boy obeyed, and brought him the sum--incorrect.
"Now, Davie," said Donal, "you said you knew all about addition, but you have not done this sum correctly." "I have only made a blunder, sir." "But a rule is no rule if it is not carried out.

Everything goes on the supposition of its being itself, and not something else.