Types vs. Sorts in HPSG

[Woo-hyoung Nahm]

Hi,

I thought 'sorts' and 'types' meant the same thing in HPSG, when they
say it models linguistic signs in terms of "typed" or "sorted" feature
structures (Pollard & Sag 1994: p8 & p17-18).

A few days ago, a question has arisen in class, whether
HPSG grammarians use those terms interchangeably without making any
technical distinction.  Are they referring to the same theoretical concept
(i.e.,'kinds' or 'classes') or do you distinguish them in some ways?
If they refer to different grammatical "sorts" :), would you explain to me
how they are different?

Thank you.

Woo-hyoung Nahm
Linguistic Dept.
Univ. of Illinois-Urbana-Champaign