When thinking about designing with future states, a designer might consider the future in the following meaningful units.
Possible futures include anything that may potentially happen. Possible futures include anything out to the level of bizarre science-fiction or what the most shocking imaginary can muster. Possible futures would include events that are exceedingly rare, similar to Nassim Nicholas Taleb’s Black Swan events, or a singularity-type event.
Plausible futures represent a narrower scope, those things that are believable given the current set of trajectories at play. Plausible futures might represent possible extensions of current trends in technology resulting in breakthrough developments, or an extension of a later confluence of current trends that results in a transformational scenario.
Probable futures are an estimation of what will most likely happen based upon an understanding of our present situation and current trends that are at play. Business refers to this as descriptive forecasting. Probable futures are often thought of as the present, but better. Some examples: cars will likely become moderately more fuel-efficient, solar energy technology will become more efficient and less costly, current trends of microchip development (aka Moore’s Law) are likely to continue.
Preferable futures represent the imagined future state toward which we would like to see the trajectory bend. The importance of preferable futures to design is embodied in Herbert Simon’s formulation of design, “devis[ing] courses of action aimed at changing existing situations into preferred ones”.
Henchey, Norman (1978) Making sense of Future Studies. Alternatives. 7. 24-29
Hancock, Trevor & Bezold, Clement. (1994). Possible futures, preferable futures. The Healthcare Forum journal. 37. 23-9.