Whitemoon, you're most welcome for the help. In answer to your question, your example sentence That you should say so surprises me is NOT a complex sentence:
A complex sentence has an independent clause joined by one or more dependent clauses.Notice that the operative phrase there is 'joined by'. Now, ask yourself, is the independent clause below joined by a subordinate clause?
Ex: That you should say so surprises me.The answer is a resounding NO. Your apparent subordinate clause that you should say so is not joined to anything; it functions as a primary constituent of the sentence: it's the subject, which is followed by a verb and its object which makes a simplex sentence (SVO):
Ex: That you should say so surprises me.Your example sentence, while it houses an elliptical noun clause (which can be interpreted as a subordinate clause) that clause is not dependent: the sentence as a whole does not house both an independent clause and a dependent clause. On the contrary, the subordinate clause is inside the main clause as one of its primary constituents, its subject:
Ex: [[You can test to see if it's a complex clause. With complex sentences, removing the subordinate clause does not render the main clause ungrammatical, because the subordinate clause is dependent (which is why it is also called a dependent clause), but removing the subordinate clause that you should say (which, by the way, is not a dependent clause because it is a primary constituent of the sentence)does indeedrender the sentence ungrammatical:
That you should say so]
Ex:That alone should tell you that your example sentence is not complex; however, if you wish to call it a complex sentence, then you should go right ahead and do so, but you'd be mistaken.
Note, in reference to your latest request,
How would answering Yes or No help you to understand that the subject in your example sentence is not joined to an independent clause; i.e., that your example sentence is complex? It's not.
Originally Posted by whitemoon