From observed to unobserved
On the axis: Scientific method · the inference from observed to unobserved
A general law extends to all cases what has been established of only a few: that the sun has always risen does not prove it will rise tomorrow, for nothing guarantees that the unobserved will behave like the observed, nor the future like the past. No accumulation of evidence fills this gap: it is the challenge each method must meet in its own way.
Justification
The problem of brings Hume to the edge of : if no reasoning justifies expecting the future to resemble the past, our most assured beliefs rest on custom, an instinct, not on reason. But the argument does not end in Pyrrhonian paralysis, and that is its point: nature is stronger than doubt, compelling us to believe and act the moment we leave the study. Hume therefore opposes to thoroughgoing , untenable in life, a mitigated (academical) skepticism, a moderate reserve that confines inquiry to what experience can reach.
Enquiry Concerning Human Understanding, sect. IV-V and sect. XII (of the academical or sceptical philosophy) · A Treatise of Human Nature, I, part IV, sect. 1-2
Anchors: Hume
leads to: Relation to certainty (Will tomorrow resemble yesterday?)