The castle in the air is generalised and abstract. In total contrast, the castle in the market place is a particular castle, made from concrete materials. You would fall through the floor of an abstract castle. The first embodiment, the first castle on the ground, is composite in nature. The general ideas come down to earth in it, a vertical descent into reality. But it must have its windows open towards the market place. While being true to its vertical fall-out of ideas, it must incorporate those practical and commercially orientated features, fed across horizontally, that will make it saleable. The first embodiment stands on that common ground where the particular and general meet. The horizontal and vertical intersect in a distinctive pattern. And the danger is that the common ground may become a battle ground. There are two ways in which such a conflict becomes almost inevitable. The first is to produce and test a prototype that has its head totally in the sky, its design chosen and slanted to make the general idea its most spectacular and cleverlooking. ‘Hang the expense but knock them for six’ is its motto. The other disaster is to collect a mass of reputed essential practical points, some of them possibly self-contradictory, and insist on all of them being inflexibly and simultaneously incorporated. One is an invention no one wants and the other wants something that no one can invent.