Full Idea
Whereas particular reality statements are in principle completely verifiable or falsifiable, things are different for general reality statements: they can indeed be conclusively falsified, they can acquire a negative truth value, but not a positive one.
Gist of Idea
Particulars can be verified or falsified, but general statements can only be falsified (conclusively)
Source
Karl Popper (Two Problems of Epistemology [1932], p.256), quoted by J. Alberto Coffa - The Semantic Tradition from Kant to Carnap 18 'Laws'
Book Reference
Coffa,J.Alberto: 'The Semantic Tradition from Kant to Carnap' [CUP 1993], p.345
A Reaction
This sounds like a logician's approach to science, but I prefer to look at coherence, where very little is actually conclusive, and one tinkers with the theory instead.