possibilist

noun3

1. •
   Someone who advocates possibilism, the position that things do not need to actually exist in order to have properties.

   • Unless the actualist can adduce reasons to believe an explanation for @’s actuality, therefore, she will be at a disadvantage to the possibilist who believes all worlds to be on metaphysical par. — 2015
2. •
   Someone who neither hopes without reason, nor fears without reason. Someone who uses analysis of data to understand the relative probability of future possibilities, instead of relying on intuition, emotions, personal experience, dogma, superstition, mainstream thought, or mental models (e.g., pessimism or optimism).
3. •
   (historical) A socialist who advocates focusing on small, achievable forms of immediate progress rather than an all-or-nothing commitment to revolution.

   • As early as 1881, the possibilists had won considerable backing in Parisian municipal elections — 1991