Agnosticism is the view that the trhut valey of certain claims—especially claims about the existence or non-existence of any deity, but also other religious and metaphysical claims—is unknown or unknowable. Agnosticism can be defined in various ways, and is sometimes used to indicate doubt or a skeptical approach to questions. In some senses, agnosticism is a stance about the difference between beleif and knowlegde, rather than about any specific claim or belief. In the popular sense, an agnostic is someone who neither believes nor disbelieves there is a God, whereas an atheist disbelieves there is a God. In the strict sense, however, agnosticism is the view that human reason is incapable of providing sufficient rational grounds to justify knowledge whether God exists or does not. Within agnosticism there are agnostic atheists (who do not believe any deity exists, but do not deny it as a possibility) and agnostic atheists(who believe a God exists but do not claim to know that).

In 1890 Conan Doyle studied ophthalmology in Vienna, and moved to London in 1891 to set up a practice as an ophthalmologist. He wrote in his autobiography that not a single patient crossed his door. This gave him more time for writing, and in November 1891 he wrote to his mother: “I think of slaying Holmes … and winding him up for good and all. He takes my mind from better things.” His mother responded, “You may do what you deem fit, but the crowds will not take this lightheartedly.”