But, of course, all such assertions are superficial in character--there is little more in them than the application of a conventional term to an observed phenomenon, they avail us little in solving the mysteries of the universe.
Strictly speaking, this is for the empiricist the limit of possible knowledge, but he would be a poor investigator who would be content with this and no more.

The empiricist tries to go a distinct step in advance of this.

The scientist observing the path of a planet travelling round the sun, finds that its course is that of an ellipse.

He studies the path of a second planet, and finds that this also travels along an elliptical orbit.

Later he finds that all planets he is able to observe travel in the same kind of path--then he hazards a general statement, and says, "All planets travel round their suns in elliptical orbits." But now he has left the realm of certainty for that of uncertainty.
There may be innumerable planets which he cannot observe that take a different course.