In the nature of a conjecture, or based on a conjecture.
In conjectural statements, the French often use the Future or the Conditional, instead of the Perfect or the Pluperfect used in English.1863, Jules Festu, Practical lessons on the comparative construction of the verb in the French and English languages:
Medicine, however, has been, and still continues to be, an art so conjectural and uncertain, that our astonishment at the anxiety with which empirics have been sought after and followed is much diminished.1844, Thomas Joseph Pettigrew, On Superstitions Connected with the History and Practice of Medicine and Surgery:
Let us not assume such previous conjecturals, but rather consult and expostulate death, since death is the wages and the reward of sin.1821, Richard Franck, Northern memoirs, page 15: