"When you go along with an idea to a comedy producer he'd say, 'Well, this has got robots and spaceships, hasn't it? Well, that's drama. You have to go to the drama department with that. They do robots and spaceships.' And so you go along to somebody in the drama department and they say, 'Yes, robots and spaceships, yes, we do those. Oh, hang on, what's this line? This is a joke, isn't it? Sorry, we don't do jokes. You have to go to the comedy department for that.'" (alt.fan.douglas-adams, 8.2.94)
That the Hitchhiker epic is SF is indisputable. It deals with imaginary worlds, space travel, life on other planets and an abundance of technological and scientific inventions as clearly shown in the summary of the plot.
Carl R. Kropf discusses the Hitchhiker novels as mock SF and gives a brief summary of how the mock genre works: By the author reversing all conventions and paradigmatic expectations readers have learned to associate with the genre its ideological function is reversed as well and thus satirized. The examples of disappointed expectations are numerous, such as:
"Adams's novels begin with the apparent destruction of the Earth (...). The two humans to escape are, as one might expect, a man and a woman, and , one naturally expects, the two will eventually settle on some Edenic planet where we can watch the author work out yet another version of the Genesis myth. Unfortunately, however, (...) contrary to all established precedents, Arthur remains indifferent to her and to sex through the first three novels of the series." (Carl R. Kropf, "Douglas Adams's 'Hitchhiker' Novels", p.2)
Kropf states that "the point is obvious enough. Adams is consciously reversing the conventions of the genre. The result is a good deal of humor as, time and again, the reader's normal expectations are disappointed." (Carl R. Kropf, "Douglas Adams's 'Hitchhiker' Novels", p.2)
I disagree with Kropf's view that a "more important effect of these reversals is that Adams's novels become reflexive, commenting on the bankruptcy of the genre's paradigms and raising questions about the nature and function of the genre as it is understood in terms of the reader's response." (Carl R. Kropf, "Douglas Adams's 'Hitchhiker' Novels", p.2)
The novels certainly achieve this, but I would not put this effect above their humorous or even philosophical quality. Kropf contradicts himself by, on the one hand, explaining how inconclusive mock SF ought to be and, on the other hand, pointing out the story of Agrajag, which is an example of the contrary in DNA's work. In "The Hitch Hiker's Guide to the Galaxy" a bowl of petunias is created in mid-air and Adams tells us "Curiously enough, the only thing that went through the mind of the bowl of petunias as it fell was Oh no, not again. Many people have speculated that if we knew exactly why the bowl of petunias had thought that we would know a lot more about the nature of the universe than we do now." (Hitch Hiker, chapter 18, p.103)
Several hundred pages later we find out and we do, in fact, know a lot more, as even Kropf admits, about the nature of the universe: "For Agrajag, Arthur is the meaning of life, (...) is "how it all turns out". (...) Agrajag (...) stands in relation to Arthur as the reader does to Adams and as humanity does to the Creator of the universe. Arthur, Adams, and God are the creators of the respective worlds which Agrajag, the reader, and all sentient beings are trying to understand." (Carl R. Kropf, "Douglas Adams's 'Hitchhiker' Novels", p.7-8)
All Arthur can do is to claim it was a coincidence and disclaim responsibility, God can only "apologize for the inconvenience" and DNA reasonably, but also tongue in cheek, explains the 'interconnectedness' between all things and a lot about parallel universes and coincidences. At the same time he puts forward a relaxed view of life and how to make the constant search for the meaning of it a little easier to the reader.
Why Carl R. Kropf could not see that DNA not merely wanted to write SF without any plan and seemingly inconclusive is easily explained by the fact that "Mostly Harmless" ties up many loose ends, best to be seen at the logical continuation of Arthur's vendetta against Agrajag, which finally comes to an end and brings with it the forseeable end of the whole saga.