2. That the differences which exist between the individual languages of those continents may be explained consistently with the proofs of original unity, by causes still in operation.
In this place, the principles appealed to in elucidation of these propositions may be explained with advantage.
1. As regards the proofs adduced of the original unity of the languages of the four continents.
These proofs are in no instance founded upon speculation or surmise. They consist in every instance, either of a comparison of terms absolutely identical in sound and sense, or of terms, of which the mutual connexion is equally certain, in accordance with those principles, with respect to which philosophical writers on language are agreed. Terms belonging to two different continents have been compared in those instances only, in which the affinities are of the same nature, as those which have been shown to be characteristic of words belonging to different dialects of the same language, in the writings of Court Ghebelin, Horne Tooke, Adam Smith, Dugald Stewart, Humboldt, and Du Ponceau. These great writers do not belong to the class of Philological speculators, but to that of authorities on the origin and mutations of human tongues.
Hence it follows that the leading doctrine laid down by Lord Bacon as applicable to the investigations of Physical science applies equally in this instance to the researches of the Philologist; I allude to the following fundamental maxim: Experience is the only legitimate guide to _Truth_; hence an accurate investigation of those facts which are _within_ the limits of our historical knowledge, forms the only admissible basis of deduction, with respect to those facts which are _beyond_ the range of our actual experience.
2. Not less applicable is the same maxim in elucidation of the second proposition, viz.: “That the differences which exist between individual languages may be explained, consistently with the proofs of original unity, by causes still in operation.”
This principle may be applied in the following manner:
There are certain languages of which the original unity can be proved, either by the extrinsic evidence of history, or by the gradual approximation they display as we ascend from modern to earlier epochs, and compare modern with _ancient_ specimens. We can show, by means of the like evidence, the progressive changes they have undergone, and the nature of the existing differences which have been the result of those changes.