Was he [Francis] the author of the Letters of Junius? Our own firm belief is that he was. The evidence is, we think, such as would support a verdict in a civil, nay, in a criminal proceeding. The handwriting of Junius is the very peculiar handwriting of Francis, slightly disguised. As to the position, pursuits, and connections of Junius, the following are the most important facts which can be considered as clearly proved: first, that he was acquainted with the technical forms of the secretary of state's office; secondly, that he was intimately acquainted with the business of the war office; thirdly, that he, during the year 1770, attended debates in the House of Lords, and look notes of speeches, particularly of the speeches of Lord Chatham; fourthly, that he bitterly resented the appointment of Mr. Chamier to the place of deputy secretary-at-war; fifthly, that he was bound by some strong tie to the first Lord Holland. Now, Francis passed some years in the secretary of state's office. He was subsequently chief clerk of the war office. He repeatedly mentioned that he had himself, in 1770, heard speeches of Lord Chatham; and some of these speeches were actually printed from his notes. He resigned his clerkship at the war office from resentment at the appointment of Mr. Chamier. It was by Lord Holland that he was first introduced into the public service. Now, here are five marks all of which ought to be found in Junius. They are all five found in Francis. We do not believe that more than two of them can be found in any other person whatever. If this agreement does not settle the question, there is an end of all reasoning on circumstantial evidence.[46][!--Note--]
Here the five points or marks of similarity between the writer of the letters and Philip Francis are of such diversity that it would be an extraordinary coincidence if there had happened to be two men whom they would fit: where so many lines converge so closely at a single point it would hardly be possible for them to meet on more than one person.
The following brief extract from Webster's argument in the White Murder Case shows the same sort of convergence of similarities: each circumstance in itself is hardly strong enough to furnish ground for an argument on analogy, but taken all together they point irresistibly in one direction, namely, to the fact of a conspiracy.
Let me ask your attention, then, in the first place, to those appearances, on the morning after the murder, which have a tendency to show that it was done in pursuance of a preconcerted plan of operation. What are they? A man was found murdered in his bed. No stranger had done the deed, no one unacquainted with the house had done it. It was apparent that somebody within had opened, and that somebody without had entered. There had obviously and certainly been concert and cooperation. The inmates of the house were not alarmed when the murder was perpetrated. The assassin had entered without any riot or any violence. He had found the way prepared before him. The house had been previously opened. The window was unbarred from within, and its fastening unscrewed. There was a lock on the door of the chamber in which Mr. White slept, but the key was gone. It had been taken away and secreted. The footsteps of the murderer were visible, outdoors, tending toward the window. The plank by which he entered the window still remained. The road he pursued had thus been prepared for him. The victim was slain, and the murderer had escaped. Everything indicated that somebody within had cooperated with somebody without. Everything proclaimed that some of the inmates, or somebody having access to the house, had had a hand in the murder. On the face of the circumstances, it was apparent, therefore, that this was a premeditated, concerted murder; that there had been a conspiracy to commit it.[47][!--Note--]
The strength of reasoning from circumstantial evidence lies in the number and the diversity of the points of similarity to the point in hand. If there are few of them, the possibility of coincidence increases, as it also does when the points of similarity come from the same source or are of the same nature. This possibility of coincidence is a good rough test of the value of reasoning from circumstantial evidence: where the theory of a coincidence would stretch all probabilities one may safely leave it out of account.
In practice the argument from circumstantial evidence is more frequent in the experience of lawyers than in that of other men; but sooner or later everybody has to pass on such reasoning, for wherever direct evidence is out of the question it may be necessary to piece the situation together by circumstantial evidence. There is some prejudice against such evidence, springing from reported cases of miscarriage of justice in convictions based on it. Such cases, however, are very rare in reality, and probably do not equal in number the cases in which mistaken or false direct testimony has caused injustice.
46. Some Pitfalls of Reasoning—Ambiguity. I have already spoken of some of the dangers to which reasoning is subject—false analogy, faulty generalization of various kinds, and various sins against the rules of the syllogism. There are still a few general dangers to speak about. It should be noted that the various kinds of fallacies run into each other, and not infrequently a given piece of bad reasoning can be described under more than one of them.
Of all the sources of faulty and misleading reasoning, ambiguity is the most fruitful and the most inclusive.
It springs from the facts that words, except those which are almost technically specific, are constantly used in more than one sense, and that a great many of the words which we use in everyday life are essentially vague in meaning. Such common words as "liberty," "right," "gentleman," "better," "classic," "honor," and innumerable others each need a treatise for any thorough definition; and then the definition, if complete, would be largely a tabulation of perfectly proper senses in which the words can be used, or a list of the ways in which different people have used them. Besides this notorious vagueness of many common words, a good many words, as I have already shown (p. 54), have two or more distinct and definable meanings.
Strictly speaking, the ambiguity does not inhere in the word itself, but rather in its use in an assertion, since ambiguity can arise only when we are making an assertion. It has been defined as "the neglect of distinctions in the meaning of terms, when these distinctions are important for the given occasion."[48][!--Note--] Suppose, for example, you are arguing against a certain improvement in a college dormitory, on the ground that it makes for luxury: clearly "luxury" is a word that may mean one thing to you, and another to half of your audience. By itself it is an indefinite word, except in its emotional implication; and its meaning varies with the people concerning whom it is used, since what would be luxury for a boy brought up on a farm would be bare comfort to the son of wealthy parents in the city. Indeed the advances of plumbing in the last generation have completely changed the relative meanings of the words "comfort" and "luxury" so far as they concern bathrooms and bathtubs. In the case of such a word, then, the weight of the definition above falls on the last clause, "when these distinctions are important for the given occasion"; here is a case where the occasion on which the word "luxury" is used determines nearly the whole of its meaning. In practice, if you have a suspicion that a word may be taken in another sense than that you intend, the first thing to do is to define it—to lay down as exactly as possible the cases which it is intended to cover on the present occasion, and the meaning it is to have in those cases. For good examples of this enlightened caution, see the definitions on pages 54-65, especially that from Bagchot.