Whenever one acts as a general agent he is supposed to have all the authority that general agents possess who thus act for their principals, unless the person who is dealing with him knows of the restriction on his authority. Suppose one goes to the office of a general insurance agent to get insurance on his home. A policy is taken and afterwards the house burns up. The company declines to pay because the agent made a lower rate than was authorized by his company. The insured however knew nothing about the restriction, and supposed that the agent had the same authority as other insurance agents have concerning rates. The company would be obliged to pay. But if the insured knew that restrictions had been put on the agent and that he was violating them in giving him the lower rate, the company would not be liable.

One who deals with a special agent must find out what authority he possesses; therefore more care is needful in dealing with a special than with a general agent. His authority must be strictly pursued. Thus it is said that a person dealing with him "acts at his own peril," is "put upon inquiry," "is chargeable with notice of the extent of his authority," "it is his duty to ascertain," "he is bound to inquire," "and if he does not he must suffer the consequences."

In some cases the law creates an agency. Thus an unpaid vendor of goods sometimes has authority to sell them, so has a pledgee of goods outside the authority conferred by the contract pledging them. A married woman whose husband does not supply her has a limited power to buy necessaries on her husband's credit, which prevails notwithstanding any objection he may make. A minor sometimes has the same power.

A person can act as an agent for another who cannot act for himself. Minors therefore can thus act. Besides individuals, corporations often act for others.

The authority of an agent may be given in writing, a power of attorney so called, or he may act, and often does, without written authority, especially a general agent. To this rule there is one well understood exception. If an agent is required in executing his authority to sign a deed or other writing, especially a sealed writing, his authority must also be equally great. In executing a deed therefore his authority must be in writing under seal, and when the deed is recorded, the agent's written authority should also be recorded; this is the usual practice. If this is not done, some person who afterward wished to purchase the land might object because the recorded title was defective.

A particular usage or custom also affects an agent's powers. If the principal confers on him authority to transact business of a well-defined nature, bounded by well-defined usage and customs, the law presumes the agency was created with reference to them. This protection affects agents and third persons alike, the latter therefore who act in good faith in such dealings are protected against secret limitations of which they had no notice.

An agent has no authority to purchase his principal's property. To do this, in a sense, would be to purchase of himself. The temptation to do this is sometimes very great, too great for him to withstand, and so he resorts to a crooked method for accomplishing his end. He sells the property to another party who afterward sells it back to him. The worst violators of this principle have been railway receivers, who have taken advantage of their position to get control of the property entrusted to them at a sum much less than its real value. Such sales can be set aside by proper legal procedure. By the modern rule they are not void but are voidable, that is, can be set aside if the creditors or other interested parties wish to do so.

Whenever therefore one deals with a general agent and his authority is disputed, unless there be restrictions known to the person dealing with him, the liability of his principal turns on the answer to the general question, what authority do general agents like himself have. This is simply a question of fact, to be determined like every other question of fact by the court in which the controversy is pending.

Another way of rendering a principal liable for the act of his agent is by ratifying it. Suppose A professed to be the agent of B in building a house for C, and built it so badly that C sued B to recover damages, whose defense was, that A was not his agent. Suppose, however, that B accepted payment for the house, this would be a ratification of A's authority to act for B even if he did not have proper authority in the beginning. Suppose A had authority to sell goods for B but not to collect payment, and someone should pay him and he ran off with the money, could his principal still collect the money of the buyer of the goods? This is a hard case, and has happened many times. The buyer usually is required to pay the second time. But if B, notwithstanding his direction to his agent not to collect payment, should receive it such conduct would operate as a ratification.

Whether the authorized act arises from a contract or from a wrong or tort, whoever with knowledge of all the facts adopts it as his own, or knowingly appropriates the benefits, which another has assumed to do in his behalf, will be deemed to have assumed responsibility for the act. Of course, such action does not render an act valid that was invalid before; its character in this respect is not changed by anything the ratifier may do.