The construction of a Universal Source Thesaurus (UST) is suggested. Unlike a universal classification, UST's main purpose would not be to serve as an indexing language to be applied directly on an universal scale but to:
(a) serve as a source in the construction of special schemes;
(b) serve as a concordance between a great many classification schemes, existing ones as well as
new ones.

The following problems arising in the planning for UST are dealt with briefly:
(1) The structure of UST—UST would have to be as complete and detailed as possible.
(2) The use of UST in the construction of special schemes—especially the "extraction" of special
schemes.
(3) The use of UST as a concordance or "switching language" between different classification
schemes as a basis for cooperative cataloguing and the possibility to have special schemes
common to a group of related institutions (semiuniversal classifications).
(4) Organization and management of UST.