The most accepted view is that a sub-clause is an explicitly predicative structure with a subject and a predicate. Many scholars hold that a clause needn’t have explicit predication (H. Poutsma, G.Curme, M.Bryant, R. Long, etc.). They treat participial, gerundial and infinitival complexes as undeveloped verbid sub-clauses (Timothy had left a lot of money, with nobody in particular to leave it to (J. Galsworthy). Prof. Y.G.Birenbaum treated participial, nounal, adjectival phrases introduced by the conjunctions while, unless, when, until as elliptical sub-clauses (He will continue talking until stopped. When traveling I have now and then watched the sunrise). We can transform these sentences into complex sentences with sub-clauses ( Until they stopped him, he will continue talking. When I was traveling, I now and then watched the sunrise). Still most linguists find these formations merely phrases, carrying implicit predicative relations.