One of the most frequent sources of mistaken views in economical science, arises from confounding the nature of _universal_ with that of _general principles_. § _Universal principles_, such as the fact that every number ending with the figure five is itself divisible by five, rarely occur except in the exact sciences. Universal principles are those which do not admit of a single exception. _General principles_ are those which are much more frequently obeyed than violated. Thus it is generally true that _men will be governed by what they believe to be their interest_. Yet it is certainly true that many individuals will at times be governed by their passions, others by their caprice, others by entirely benevolent motives: but all these classes together, form so small a portion of mankind, that it would be unsafe in any inquiry to neglect the great principle of self-interest. Notwithstanding, however, all the exceptions we may meet with, it is impossible to take any just views of society without the admission of general principles, and on such grounds they will be used in these pages. Self-interest, combined in various degrees with knowledge, assumes the most diversified forms. It excites our contempt or raises our admiration, according to the littleness or the greatness of the object it pursues—according to the temporary or the more distant advantages it seeks. On the one hand, it governs the minister of a party on his doubtful eminence, whilst on the other it guides the enlightened statesman to the object of his distant ambition. § Again, it is admitted as a general principle that _each man is the best judge of his own wants and of his own interest_. Now although many individuals, and even whole classes of society, have at times been thought by more enlightened men to have formed erroneous opinions as to their true interest, yet, when it is remembered, that every man must see many views of his own case, and must know many facts connected with it, which he has not communicated even to his most confidential adviser, those who have had most experience are most inclined to believe that the exceptions are much less frequent than at first sight would appear. Another source of erroneous opinions arises from neglecting causes apparently insignificant.