"Knowing" is generally considered to imply that we think something is beyond reasonable doubt. If you can only speak of knowledge in the sense of logical entailment, the word would be useless because then nobody knows anything. Words like "maybe" and "possibly" would also become useless, because they then apply to all knowledge. A distinction that doesn't distinguish between things is not a useful distinction to make.

Reasonable doubt is a legal term, not a scientific one.