It frequently happens that two persons, reasoning right on a mechanical subject, think alike and invent the same thing without any communication with each other.

Richie and Eddie couldn't exist without each other. They're two halves of the same person.

It not infrequently happens that persons without any other special qualification than the drama of their lives are precipitated into important political positions.

Two persons cannot long be friends if they cannot forgive each other's little failings.

No two persons ever read the same book.

Whenever the nature of the subject permits the reasoning process to be without danger carried on mechanically, the language should be constructed on as mechanical principles as possible; while in the contrary case it should be so constructed, that there shall be the greatest possible obstacle to a mere mechanical use of it