You are right about the quote. It seems that what Russell considers definite knowledge is ... answer can be found in the laboratory. It depends on what is the

You are right about the quote. It seems that what Russell considers definite knowledge is ... answer can be found in the laboratory. It depends on what is the best available method for proving, to the extent to which this is possible, a given hypothesis. Whenever an experimental method in the scientific sense is possible, then he considers that kind of knowledge definite. I agree that the fact that it is also provisional is confusing, but I think that it's just a matter of language in this case, maybe definite is not the best word. I agree that maybe his definition is not fully satisfactory. But this book's audience is lay people like me, it is not as much an academic work as a book of popular philosophy (like popular science). For this reason, he probably preferred to write engaging prose, rather than being totally precise but dry. I posted this quote because whenever there is an article about philosophy in HN, people invariably enter a debate as to what exactly is philosophy. I find that for the lay man his definition is very clear, simple, memorable and beautifully written. I find it very useful in practice, for people like me it is a powerful definition.