which in ordinary life is expressed by saying: "If it were true, we should have heard of it;" it implies a general proposition which may be formulated thus: "If an alleged event really had occurred, there would be some document in existence in which it would be referred to."
In order that such reasoning should be justified it would be necessary that every fact should have been observed and recorded in writing, and that all the records should have been preserved. Now, the greater part of the documents which have been written have been lost, and the greater part of the events which happen are not recorded in writing. In the majority of cases the argument would be invalid. It must therefore be restricted to the cases where the conditions implied in it have been fulfilled.
(1) It is necessary not only that there should be now no documents in existence which mention the fact in question, but that there should never have been any. If the documents are lost we can conclude nothing. The argument from silence ought, therefore, to be employed the more rarely the greater the number of documents that have been lost; it is of much less use in ancient history than in dealing with the nineteenth century. Some, desiring to free themselves from this restriction, are tempted to assume that the lost documents contained nothing interesting; if they were lost, say they, the reason was that they were not worth preserving. But the truth is, every manuscript is at the mercy of the least accident; its preservation or destruction is a matter of pure chance.
(2) The fact must have been of such a kind that it could not fail to be