This matter of the _Ding an sich_ Ferrier felt to be the crucial point in his system: 'You talk glibly of "existence _per se_," as maids of fifteen do of puppy dogs. This shows that, like a carpet knight, you have never smelt the real smoke of metaphysical battle, but at most have taken part in the sham fights and listened to the shotless popguns of the martinet of Königsberg. You will find existence _per se_ a tougher customer than you imagine.' As to the _Institutes_, then on the verge of publication, the author says: 'I am inclined to follow your advice, so far, in regard to the title of the work, and to call it the "Theory of Knowing and Being," leaving out ignorance. But why an _introduction_ to metaphysics? If this be an _introduction_ to metaphysics, pray, Mr. Pundit, what and where are metaphysics themselves? No, sir, it shall be called a _text-book_ of metaphysics, meaning thereby, that it is a complete body (and soul) of metaphysics. You are an uncommonly _modest_ fellow in so far as the protestations of your _friends_ are concerned!' This correspondence appears to have continued regularly for some years, and to have dealt almost entirely with metaphysical and economic subjects--the subjects which were constantly in Ferrier's mind, as he taught them in the University and tried to work them out in his study. Doubtless it was of the greatest use to him to be able to write about them as he would, had opportunity served, have spoken; and this opportunity was afforded by his friendship with his correspondent, whose interest in philosophy was keen, and whose critical faculties were exceptionally acute, although he never accomplished any original work on philosophical lines. Of other letters few have been preserved. Absence from home did not make a reason for writing, for Ferrier's journeyings were but few. In 1859, however, he made an expedition to England to see his newly-married daughter, Lady Grant, start for India with her husband, Sir Alexander Grant, after his appointment to the Chancellorship of the University of Bombay. From Southampton he made his way to the scene of his schooldays at Greenwich, from which place he writes to one of the sons of Dr. Bruce of Ruthwell, with whom he spent a happy childhood: 'One of our fêtes was a sumptuous fish dinner at Greenwich. I call it sumptuous, but in truth the fish was utter trash, the best of them not comparable to Loch Fyne herring. Whitebait is the greatest humbug of the age, though it may be heresy to say so in your neighbourhood.' This journey was concluded by a visit to Oxford and to the Lake country, with both of which Ferrier's associations were so many and so agreeable.