This paper aims at studying the classic detective Sherlock Holmes as a unity of ‘the two cultures’, science and aesthetics, and further extending to consider man and machine. Arthur Conan Doyle’s Sherlock Holmes is armed with scientific knowledge and keenly analytical power, and these factors led to him being regarded as ‘a thinking machine’. However, his character is based on the empirical rationalism of Enlightenment and the aesthetic imagination of Romanticism, which are related to the origin of the detective novel. Holmes’s ambivalence contains two seemingly conflicting elements, science and the arts. That provides a new point to reconsider thoughts that we have had about humanity and the relationship between human and machine(non-human). In the age of posthumanism, Sherlock Holmes can be a model as a hybrid, having balance between ‘the two cultures’ and the possibility to newly explore humanity.