Adjective : a tenable theory. ,a research grant tenable for two years.    From Dictionary.com. 

Striking it is, that even Lessing should cling to such definitions and employ all his ingenuity to prove their tenableness.    From Wordnik.com.  [The German Classics of the Nineteenth and Twentieth Centuries, Volume 09 Friedrich Hebbel and Otto Ludwig] Reference

What then is to be said of the tenableness of such a position?.    From Wordnik.com.  [On Compromise] Reference

It was during this course of reading that for the first time a doubt came upon me of the tenableness of Anglicanism.    From Wordnik.com.  [Apologia Pro Vita Sua] Reference

It was during this course of reading that for the first time a doubt came upon me of the tenableness of Anglicism, and by the end of August I was seriously alarmed.    From Wordnik.com.  [The World's Greatest Books — Volume 13 — Religion and Philosophy] Reference

Theology and speculative philosophy went on their courses unheedful of these developments of physical science, until in our day both have had to reconsider the tenableness of their position, and to see that Nature and its physical manifestations have to enter as all-important factors into their reconstructions.    From Wordnik.com.  [An Interpretation of Rudolf Eucken's Philosophy] Reference

Wonderfully active, wonderfully quick and receptive, full of imagination and of the power of combining and constructing, and never wearied out or dispirited, his mind took in large and grand ideas, and developed them with enthusiasm and success, and with all the resources of wide and varied knowledge; but the affluence and ingenuity of his thoughts indisposed him, as it indisposes many other able men, to the prosaic and uninteresting work of calling these thoughts into question, and cross-examining himself upon their grounds and tenableness.    From Wordnik.com.  [Occasional Papers Selected from the Guardian, the Times, and the Saturday Review, 1846-1890] Reference