English: farther vs further

Self-tutoring about English: the tutor mentions a distinction between farther and further.

The following is by my understanding.

I always thought farther and further were interchangeable, but it seems I was wrong.

Apparently, farther refers to actual distance: In one hour, the speedboat traveled farther than the tugboat. However, further means to a greater extent: They opted for further discussion about the proposed traffic pattern.

Interesting, eh?

Source:

Sabin, W.A. (1986). The Gregg Reference Manual. McGraw-Hill Ryerson Limited.