One cause of figurative language is found in the similarity of effects produced on the body by operations of mind and operations of matter. Whatever causes affect the mind in a similar manner are called by the same name. Thus, when a man endeavors to penetrate a hard substance, the muscles of his head and neck are affected in a particular manner. The same muscles are affected in a similar way when a person makes powerful and reiterated efforts to comprehend a difficult subject. Both these actions, therefore, are called by the same name, and a man is said to _penetrate_ the wood with an instrument, or to _penetrate_ into the subject of his investigations. Thus joy is said to _expand_ the breast, because it does, in fact, produce a sensation which resembles this action. There is a great variety of figurative language founded on this principle. Indeed, there is little said respecting the mind, and its qualities and operations, where we do not apply terms that describe the qualities, actions, and relations of matter. It is also the case that _actions_ and _relations_ that resemble each other are called by the same name, without regard to the objects in which they exist. Thus the skies are said _to weep_. Here there is, in fact, the same action as is weeping in mankind, and it receives the same name, though it is connected with a different subject. Thus, also, the sword is said to be "_drunk_ with the blood of the slain." Here the same relation exists between the blood and the sword as between a man and an immoderate quantity of liquor, and the relation receives the same name in each case. _An allegory_ is a succession of incidents and circumstances told of one thing which continually recall another thing, which it resembles in the particulars mentioned. Thus the aged Indian chief describes himself by an allegory: "I am an aged hemlock. The winds of a hundred years have swept over its branches; it is dead at the top; those that grew around have all mouldered away." _A parable_ is of the same character as an allegory. _A type_ is an object of conception in which many of its qualities and relations resemble another object that succeeds it in regard to _time_. _Hyperbole_ is a collection of actions, qualities, or circumstances ascribed to an object which are contrary to the laws of experience, and this language is employed to express excited feeling. Thus, by hyperbole, a person is said to be "_drowned_ in tears." _Irony_ is language used in such a manner as to contradict the known opinions of the speaker, and is intended to represent the absurdity or irrationality of some thing conceived by him. _Symbols_ are material things employed to convey the ideas of one mind to another. Thus, as the cultivation of the olive is connected with seasons of peace, an olive branch is used to express the idea of peace.