Definitions are sometimes explained as being of two kinds--of things and words. The definition of _words_ is the explanation of the sense in which they are used. The definition of _things_ is an explanation of the specific properties by which they differ from all other things. To define a thing, says Dr. Watts, we must ascertain with what it agrees, then note the most remarkable attribute of difference, and join the two together. Probity--the disposition to acknowledge the rights of mankind. Justice--the disposition to maintain the rights of mankind. Benevolence--the disposition to improve the rights of mankind. Deceit--the concealed violation of the rights of mankind. Injustice--the open violation of the rights of mankind. Malevolence--hatred of the rights of mankind. In defining a word we seek some class to which to refer it, that we may identify it, and fix attention upon that peculiarity by which we can distinguish it from all other things. 'Probity and 'justice' are referred to 'disposition,' with reference to the 'rights of mankind' as their sphere of existence: and _acknowledgment, and maintenance_, are mentioned as the distinguishing features. Distinctions must not be made without differences. The definition should be plainer than the thing defined. Aristotle's definition of motion is considered defective in this respect:--'Motion--an act of a being in power, so far forth as it is in power.' Tautological definitions cause more to be supposed than is true--the too terse explanation leaves some necessary thing unmentioned. A perfect definition requires the union of the concise, the clear, and the adequate. Some persons are so unskilful in the analysis of terms as to occasion the advice _Nil explicare_--never explain yourself if you wish to be understood. Double meanings should be avoided. The writer may himself alternate in their use, and the reader may take the word in the unintended meaning. All men have not the strong sense of Johnson. When Caleb Whiteford inquired seriously of the Doctor, whether he really considered that a man ought to be transported, like Barrington, the pickpocket, for being guilty of a double meaning. 'Sir,' said Johnson, 'if a man means well, the more he means the better'--which, whether real or fictitious, is one of the happiest answers that ever crushed a quibble.* * Hood's Own. I have frequently put the question--What is consciousness? to persons who have been conscious for twenty or thirty years, but who were yet unable to reply. Had any one deprived these persons of consciousness, a judge would have hanged him for the offence; yet, could they themselves have been interrogated as to what harm they had suffered, they could not have told what they had lost. And upon the principle, that he not knowing what he has lost, is no loser, these persons, though murdered, had suffered no harm.