In like manner, if it be not indeed the operation of the same principle, cause suggests the effect, and effect its cause. The wound reminds me of the instrument, and the instrument awakens the unpleasant conception of the wound which it once inflicted. _Why one Conception rather than another._--Inasmuch as any one conception may awaken in the mind a great variety of other conceptions--since a picture, for example, may recall the person whose likeness it is, or the artist who painted it, or the friend who possesses it, or the time and place in which it was sketched, or the room in which it formerly hung, or any circumstance or event connected with it--the question arises, why, in any given instance, is _one_ of these conceptions awakened in the mind rather than any _other_ in its stead? It is evident that the action of the associating principle is not uniform, sometimes one conception being awakened, sometimes another. _Secondary Laws._--In answer to this, Dr. Brown has shown that the action of these general and primary laws of suggestion, now named, is modified by a variety of circumstances, which may be called _secondary_ laws of suggestion, and which will account for the variety in question. These modifying circumstances are: 1. Continuance of attention. 2. Vividness of feeling. 3. Frequency of repetition. 4. Lapse of time. 5. Exclusiveness of association. 6. Original constitutional differences. 7. State of mind at the time. 8. State of body. 9. Professional habits. Any one of these circumstances may so modify the action of the primary laws of suggestion, that one conception shall be awakened in the mind rather than another, by that which has preceded. _Correctness of this View._--There can be little doubt as to the correctness of this view. The attention, for example, which a given object or event excites at the time of its occurrence, and the strength and liveliness of feeling which it awakened in us, have very much to do, as every one knows, with our subsequent remembrance of that object or event. So also has the frequency with which the train of thought has been repeated--a fact illustrated in the process of committing to memory. The more frequently two things come together before the mind, the more likely will it be, when one is again presented, to think of the other. In the process of learning a thing by rote, we repeat the lines over and over, until they become so associated, and linked together, that the suggestion of one recalls the whole. Frequently, however, we find it difficult to pass from one sentence to another, or from one stanza or paragraph to another, while we find no difficulty in completing the sentence or paragraph once commenced. The reason is, we have repeated each sentence or stanza by itself in the process of learning, and have not connected one with another. The last words of one sentence, and the first words of another, have not been repeatedly conjoined in the mind--have not frequently _coëxisted_.