The incident occurs in The Naval Treaty, and is surely one of the most memorable (and the strangest) in the Canon. In the middle of an investigation, Holmes suddenly starts philosophizing about a rose that he’s seen in the garden.
“‘What a lovely thing a rose is!’
“He walked past the couch to the open window and held up the drooping stalk of a moss-rose, looking down at the dainty blend of crimson and green. It was a new phase of his character to me, for I had never before seen him show any keen interest in natural objects.
“‘There is nothing in which deduction is so necessary as in religion,” said he, leaning with his back against the shutters. “It can be built up as an exact science by the reasoner. Our highest assurance of the goodness of Providence seems to me to rest in the flowers. All other things, our powers, our desires, our food, are all really necessary for our existence in the first instance. But this rose is an extra. Its smell and its colour are an embellishment of life, not a condition of it. It is only goodness which gives extras, and so I say again that we have much to hope from the flowers.’”
Chronologists variously date this story to 1887 or 1889; my own preference is for 1888. But the point is a complicated one. The events certainly took place after those of the case known as The Sign of the Four (1887, by my reckoning), in the course of which Holmes recommended to Watson a notorious atheistical work: Winwood Reade’s The Martyrdom of Man – a controversial book in its day, rather as The God Delusion is now.
There is nothing explicitly Christian about Holmes’s sermon on the rose, so it probably pre-dates The Boscombe Valley Mystery (June 1889), in which he sounds very Christian indeed, telling a dying man, for example, that “you will soon have to answer for your deed at a higher court than the Assizes.”
I think that in The Naval Treaty we see Holmes on the very threshold of his conversion. The speech assumes that there is a supernatural creator, whom Holmes does not yet call God, but only Providence; and argues that the creation gives us evidence about this being’s character. His argument is that the flower is so perfectly designed to give pleasure to human beings that it proves benevolence in the unknown creator.
One obvious problem with this argument is that the moss-rose is not a wild flower, but one that has been selectively bred by many generations of gardeners for the precise purpose of giving pleasure to human beings. If its beauty proves anything, it proves than human beings are skilful, rather than that Providence is benevolent.
Holmes elsewhere shows a dislike of wild Nature, so perhaps it’s not surprising that he would choose what is really a man-made flower rather than a natural one. Nevertheless, his argument could be applied to wild flowers, too – and indeed to other natural formations which can be extremely beautiful. Out in splendid countryside surely everyone must sometimes experience an indistinct feeling that “Whoever is responsible for all this is admirable!” So that part of the argument (just about) works, I think — although ‘admirable’ is not quite the same as ‘benevolent’.
However, Holmes merely assumed that “Whoever” must be a transcendent God. Yet Darwin had already proved that Nature alone, without God, was quite capable of producing all the complex life-forms that we see about us. Flowers, for example, have evolved to attract insects: their forms and their patterns are shaped for that purpose. The most obvious answer as to why flowers are attractive to us would seem to be because we and insects have a good deal in common – they are cousins of ours, after all!
So why did Holmes, who was no fool, fail to see this?
Well, I think that it was a case of wishful thinking. In The Cardboard Box (which I date to August, 1888) Holmes had exclaimed: “What object is served by this circle of misery and violence and fear? It must tend to some end, or else our universe is ruled by chance, which is unthinkable. But what end? There is the great standing perennial problem to which human reason is as far from an answer as ever.” The human suffering which he saw in the course of his work distressed him deeply, and he wanted there to be something beyond the visible world which would make sense of it all. The dominant religion of his day, Christianity, offered an attractive solution: that a benevolent God had created the world, and would provide an afterlife in which all injustices would be put right.
My experience of people who are under the influence of cocaine is that they are prone to talk very freely about ideas that seem attractive to them, and cannot be made to consider the case against such ideas. (This is rather different to the effect of cannabis, which seems to make people more open-minded.) We know, of course, that the late 1880’s were the years in which Holmes’s cocaine-addiction was at its worst. I suggest that it was a combination of cocaine and wishful thinking which inspired his sermon on the rose.
These ideas are explored in more detail in my novel, A Case of Witchcraft, which you should definitely read!