I ordered this book from Amazon after reading Daniel Wegner's 'The Illusion Of The Conscious Will', in which a passage from Twain's book appeared. Until then I had not heard of it. As I, myself, believe in human free will and in genuine moral responsibility, I am interested in all those thinkers who believe in the contrary idea that man is essentially a machine. These remarks on Twain's 'What Is Man' should be understood against that background, in terms of what I, personally, hoped to get from reading it.
The book is devoted entirely to the explicit thesis that man is a machine. Twain doesn't present the usual materialist reasons for that belief - not for him the reductive materialism of Hobbes, La Mettrie, Diderot, d'Holbach, Buchner and Haeckel. Instead he appears to draw solely on his own experience of himself and others in daily life. Thus he believes that man is essentially a machine constructed to decide and act in ways that maximise its feeling of ease. We are, as it were, 'conscience machines', our actions being decided by our inbuilt need to attain a state of easy conscience.
You can find this idea presented in Hobbes, and Twain draws the same conclusion as Hobbes that all assessments of moral worth are thereby rendered meaningless. To me the book is valuable for being a very clear, passionate expression of this idea - with which I disagree profoundly - and which I have sometimes heard presented by people I know. Given that our acts of altruisim sometimes are tainted by selfish motives, there is perhaps a tendency in us to proceed along these lines. We need to maintain a mature, honest balance in the face of this potential cynicism, which Twain fails completely to do in this book.
The style of the book is also interesting. It is a dialogue between an Old Man (who puts forward Twain's ideas) and a Young Man who is shocked to hear it all. The Old Man speaks fiercely and with the complete certainty that he is correct. He cannot even accept that what he is putting forward is a point of view, but several times refers to it as established fact. At the start of the book Twain claims that millions of people secretly accept the correctness of his account of man as a machine - interesting, historically, if it is true, which I think it may be.
To sum up, then, this book was valuable to me because it gave a particularly clear expression of a line of thought that I have encountered in life and find significant. It was a good test of my own thinking to write down what I found wrong with it.
Finally, this is a small book - just 140 pages of height about six inches. Thus it doesn't take long to read.