The general idea is that Browning must have intended “Sludge” for an attack on spiritual phenomena, because the medium in that poem is made a vulgar and contemptible mountebank, because his cheats are quite openly confessed, and he himself put into every ignominious situation, detected, exposed, throttled, horsewhipped, and forgiven.  To regard this deduction as sound is to misunderstand Browning at the very start of every poem that he ever wrote.  There is nothing that the man loved more, nothing that deserves more emphatically to be called a speciality of Browning, than the utterance of large and noble truths by the lips of mean and grotesque human beings.  In his poetry praise and wisdom were perfected not only out of the mouths of babes and sucklings, but out of the mouths of swindlers and snobs.  Now what, as a matter of fact, is the outline and development of the poem of “Sludge”?  The climax of the poem, considered as a work of art, is so fine that it is quite extraordinary that any one should have missed the point of it, since it is the whole point of the monologue.  Sludge the Medium has been caught out in a piece of unquestionable trickery, a piece of trickery for which there is no conceivable explanation or palliation which will leave his moral character intact.  He is therefore seized with a sudden resolution, partly angry, partly frightened, and partly humorous, to become absolutely frank, and to tell the whole truth about himself for the first time not only to his dupe, but to himself.  He excuses himself for the earlier stages of the trickster’s life by a survey of the border-land between truth and fiction, not by any means a piece of sophistry or cynicism, but a perfectly fair statement of an ethical difficulty which does exist.  There are some people who think that it must be immoral to admit that there are any doubtful cases of morality, as if a man should refrain from discussing the precise boundary at the upper end of the Isthmus of Panama, for fear the inquiry should shake his belief in the existence of North America.  People of this kind quite consistently think Sludge to be merely a scoundrel talking nonsense.  It may be remembered that they thought the same thing of Newman.  It is actually supposed, apparently in the current use of words, that casuistry is the name of a crime; it does not appear to occur to people that casuistry is a science, and about as much a crime as botany.  This tendency to casuistry in Browning’s monologues has done much towards establishing for him that reputation for pure intellectualism which has done him so much harm.  But casuistry in this sense is not a cold and analytical thing, but a very warm and sympathetic thing.  To know what combination of excuse might justify a man in manslaughter or bigamy, is not to have a callous indifference to virtue; it is rather to have so ardent an admiration for virtue as to seek it in the remotest desert and the darkest incognito.