Nowhere do we find any but superficial morphological interinfluencings.  We may infer one of several things from this:—­That a really serious morphological influence is not, perhaps, impossible, but that its operation is so slow that it has hardly ever had the chance to incorporate itself in the relatively small portion of linguistic history that lies open to inspection; or that there are certain favorable conditions that make for profound morphological disturbances from without, say a peculiar instability of linguistic type or an unusual degree of cultural contact, conditions that do not happen to be realized in our documentary material; or, finally, that we have not the right to assume that a language may easily exert a remolding morphological influence on another.

Meanwhile we are confronted by the baffling fact that important traits of morphology are frequently found distributed among widely differing languages within a large area, so widely differing, indeed, that it is customary to consider them genetically unrelated.  Sometimes we may suspect that the resemblance is due to a mere convergence, that a similar morphological feature has grown up independently in unrelated languages.  Yet certain morphological distributions are too specific in character to be so lightly dismissed.  There must be some historical factor to account for them.  Now it should be remembered that the concept of a “linguistic stock” is never definitive[173] in an exclusive sense.  We can only say, with reasonable certainty, that such and such languages are descended from a common source, but we cannot say that such and such other languages are not genetically related.  All we can do is to say that the evidence for relationship is not cumulative enough to make the inference of common origin absolutely necessary.  May it not be, then, that many instances of morphological similarity between divergent languages of a restricted area are merely the last vestiges of a community of type and phonetic substance that the destructive work of diverging drifts has now made unrecognizable?  There is probably still enough lexical and morphological resemblance between modern English and Irish to enable us to make out a fairly conclusive case for their genetic relationship on the basis of the present-day descriptive evidence alone.  It is true that the case would seem weak in comparison to the case that we can actually make with the help of the historical and the comparative data that we possess.  It would not be a bad case nevertheless.  In another two or three millennia, however, the points of resemblance are likely to have become so obliterated that English and Irish, in the absence of all but their own descriptive evidence, will have to be set down as “unrelated” languages.  They will still have in common certain fundamental morphological features, but it will be difficult to know how to evaluate them.  Only in the light of the contrastive perspective afforded by still more divergent languages, such as Basque and Finnish, will these vestigial resemblances receive their true historic value.