A Comparison

Surface Tension is a story of human settlers in another world who decide to change human physiology significantly in order for their successors to survive in that world; the successors have no idea where they come from, and they piece what facts the humans made available to them to get at the truth.

Driftglass is about the pitfalls of physiological manipulation to have humans plumb the depths of the oceans to carry out complex engineering and oil rigging projects. It's a complex story of how change might sometimes only achieve a return to one's limitations, instead of transcendence.

Oceanic charts a man's journey from fledgling believer in a troubling religion and his final disillusionment through science. It too, like the two previous stories, is set in the ocean, in another planet, and the humans themselves are not aware that they may be something more.

Surface Tension by James Blish is one of the purest examples of hard science fiction. It is perhaps not as 'hard' as The Cold Equations by Tom Godwin, in which story there is very little in the way of a world-building imagination at work, but it is 'hard' in the sense that every aspect of the story seems geared towards a specific ending, and revelation. It is single minded in its endeavor to bring about a paradigm shift, or 'conceptual breakthrough'.

Oceanic by Greg Egan is similar, but it decides to shed the sense of adventure the Golden Age was so fond of for a more introspective and personal glimpse into the world of faith and science. Where it moves away from the joyous exercise of world-building, it excels in a painfully believable tale of one man's gain, and loss of faith.

Driftglass by Delany decides to walk the fine line by bringing such far flung exercises in speculation down to earth and dulling its edges down. It is what Geoff Ryman might have labeled 'mundane SF', but in being mundane it is that much more invigorating. It offers a world not unlike ours, but sufficiently unlike ours to permit a certain expenditure of energy in traversing that rift, with the intention of having that energy transmuted into a heightened awareness of our world.

In short, where the previous two stories used our knowledge of the 'real' world as a jumping off point into speculative forays, Delany does just the opposite. He begins by having taken for granted a supra-truth, and then works tirelessly to reel it in, into the murky depths of our own world.