The argument from cause to effect is most frequently employed in criminal trials. In such cases the motive for committing the crime is regarded as the cause and the crime as the effect. The argument is usually begun by proving the existence of strong motives such as an abnormal desire to acquire more money or property, to work revenge on bitter enemies, or to avert financial or domestic disaster. With these strong motives shown it is easy to connect them with the crime. This is the method of argument from cause to effect which is used by Daniel Webster in the White murder trial. He showed clearly that the Knapps believed that they could obtain the fortune of White by destroying his last will and murdering him. He argued that this was the cause which produced the effect of murder. The following extract from Webster’s speech before the jury will show the application made of the argument from cause to effect.
“When we look back, then, to the state of things immediately on the discovery of the murder, we see that suspicion would naturally turn at once, not to the heirs at law, but to those principally benefited by the will. They, and they alone, would be supposed to have a direct object for wishing Mr. White’s life terminated. And, strange as it may seem, we find counsel now insisting, that, if no apology, it is yet mitigation of the atrocity of the Knapps’ conduct in attempting to charge this foul murder on Mr. White, the nephew and principal devisee, that public suspicion was already so directed. As if assassination of character were excusable in proportion as circumstances may render it easy. Their endeavors, when they knew they were suspected themselves, to fix the charge on others, by foul means and by falsehood, are fair and strong proof of their own guilt.
“The counsel say that they might safely admit that Richard Crowninshield, Jr., was the perpetrator of this murder.
“But how could they safely admit that? If that were admitted everything else would follow. For why should Richard Crowninshield, Jr., kill Mr. White? He was not his heir; nor was he his devisee; nor his enemy. What could be his motive? If Richard Crowninshield, Jr., killed Mr. White he did it at some one’s procurement who himself had a motive. And who having any motive, is shown to have had any intercourse with Richard Crowninshield, Jr., but Joseph Knapp and this principally through the agency of the prisoner at the bar? It is the infirmity, the distressing difficulty of the prisoner’s case, that his counsel cannot and dare not admit what they yet cannot disprove, and what all must believe. He who believes, on this evidence, that Richard Crowninshield, Jr., was the immediate murderer cannot doubt that both the Knapps were conspirators in that murder.”
III. Argument from effect to effect.
An argument from effect to effect is one in which an argument from effect to cause is combined with an argument from cause to effect. To illustrate this kind of argument we may explain a simple example frequently used in this connection. A boy announces that there is skating this morning because the thermometer registers below zero. Now the thermometer registering below zero is not the cause of the skating. Both the registering of the thermometer and the skating are the effects of a common cause, viz.—low temperature. The boy has observed one of the effects and at once concludes that the other effect must exist. His is an argument from effect to effect, or to be more exact, an argument from one effect of a cause to another effect of the same cause. The whole process of reasoning involved as well as the relation between the two parts of an argument from effect to effect may be represented by the following tabulation:
A. Argument from effect to cause.
1. All times when the thermometer registers below zero are times when the temperature is far below freezing.
2. This is a time when the thermometer registers below zero.
3. Therefore this is a time when the temperature is far below freezing.