These words refer to the act of not preventing. Permit , allow and let are loosely related, permit being the strongest of the three. To permit is to grant leave to or empower by express consent; the word suggests authority that could prevent, if it so chose: The chairman recognized the delegate and permitted him to speak. Allow , used positively, means to grant as a right or privilege: a teenager allowed to stay out until midnight and permitted to use the family car on occasion. Allow and permit are often used interchangeably; allow , however, is a less formal term and often carries the idea of simply not attempting to hinder. Permit , by contrast, implies a greater or lesser degree of approval and may indicate official sanction.

• The nurse allowed the visitors to remain beyond the hospital visiting hours, though it was not permitted .

Let , the least formal of these words, may sometimes suggest permission or consent, but may imply no more than a failure to prevent or restrain.

• She asked her boss to let her leave an hour early; Don’t interrupt him – let him speak his piece.

A person may let things happen passively, either through choice or through indifference, carelessness, error or inattention.

• She decided to let her hair grow; He let his insurance policy lapse; They forgot to shut the windows and thereby let the rain in.

As opposed to permit , let may point up a lack of, or failure to exercise, preventive authority: a timid, unassertive little man, always letting people take advantage of him.

Authorize is stronger and more formal than permit and is more limited in application. It implies positive approval of a proposed course of action by an authority empowered either to permit or to forbid it.

• The government authorized the construction of a new expressway; The firm authorized the use of a company car by the salesman after working hours.

Authorize may further imply the delegation of authority: a U.N. delegate authorized by his government to conduct formal negotiations.