The dual nature of Walter Shandy's hobby-horse is portrayed: his theories and the oratory with which he tries to convince people of his theories. The most important thing in the world to Walter is a hypothesis; everything takes second place to it. He is a man with a ruling passion, dominated by one of the humours. He is the source of some of the subtle but rollicking comedy of Tristram Shandy: Walter has his theories, but no one can understand them but him. He never convinces anyone of anything, but he never stops trying. He will go to any lengths to persuade; he is as eloquent as any of the great orators of antiquity, and he instinctively knows all the tricks of elocution and delivery. But nobody is ever persuaded.
His theory of names is obviously a setup for another frustration: Tristram's third accident (the second is to his nose). Walter hates the name Tristram above all other names, and yet his son comes to be named Tristram. This fact of course provides us with a laugh, but it is also easy to see that Tristram has a purpose in introducing to us Walter's theory — even though he hasn't been born yet.
Pulling the reader into his work and sending her back to find out where he made a particular statement, Tristram has the excuse of defending his book again: it is not an adventure story, and the reader who misses a point misses something valuable. He is exaggerating grossly the importance of the point (and he knows he is): it was very trivial, and the reader could not have seen it beforehand. But he is still right — he wasn't sending her off on a wild goose chase technically.
He now therefore has the further excuse for introducing a piece of "learned jargon," a bit of arch-trivia about intrauterine baptism. Like Yorick, he is always against gravity and seriousness; he intends to ridicule and satirize the "Learned Doctors of the Sorbonne," the Catholic authorities, and he does so by reducing the suggestion to an absurdity.
Even though Tristram sees through his father's weakness, in this matter he shows himself to be very much the son of Walter Shandy, using the kind of argument that Walter himself might have used.
