Grading Science Fiction for Realism is a nice page on hard vs. soft science fiction, with the latter being the sort that approaches fantasy. Sociological SF is also called "soft SF", but it is a different sort of softness, one that's opposed to nuts-and-bolts hardness.
That page has a scale of hard-to-soft, so it's not just hard vs. soft.
* Present-Day Technology, though often with relatively small extrapolations, like technothriller secret weapons. Science fiction fades off into high-tech mundane fiction here. Lee Correy's "Shuttle Down" is a good example.
* Ultra Hard (Diamond Hard). Extrapolated present-day science and technology without being very speculative. Artificial intelligence, genetic engineering, interplanetary colonization, nanotechnology, ... The parts of "2001: A Space Odyssey" without the ET's, for instance.
* Very Hard. More speculative extrapolations, but still within well-tested theories. Relativistic spaceships, interstellar colonization, mind uploading, ...
* Plausibly Hard. Even more speculative stuff, but coexisting with well-established theories. Like faster-than-light travel with time travel, a consequence of relativity. The ET parts of "2001", for instance.
* Firm. Less plausible stuff, like FTL without time travel, but such stuff is kept to a minimum. Isaac Asimov's "Foundation", for instance.
* Medium. More such stuff, like abundant ET civilizations, ET biotas much like Earth ones, desert worlds with breathable atmospheres, ... "Dune", for instance.
* Soft. Very humanlike sentient ET's, ET cultures uniform, ... much of "Babylon 5", for instance.
* Very Soft. ET's having societies much like past and present human societies, patchy advancement of technology, technobabble, ... much of "Star Trek", for instance.
* Mushy Soft. Superhero powers, giant insects and similar monsters, energy weapons without any hint of their energy supply or energy dispersal, spaceships that battle like Earth vehicles, ...
At this end, science fiction fades off into fantasy, even if not swords-and-sorcery fantasy.