Most studies on the distribution of the null complementizers in English assume that overt that clauses and null that clauses have the identical underlying structure, where the overt/null COMP represents a C head (Stowell 1981, a.o.). This predicts that both overt and null that clauses show (nearly) the same syntactic distribution, contrary to fact. This paper explores a new outlook of overt and null complementizers in clausal complements of both non-factive and factive predicates in English, building on the assumptions that (i) feature specification on C differs from language to language and (ii ) languages also differ as to lexicalizing a subset of these features on C. Adopting Rizzi's (1997) split CP structure with two C heads, Force and Finiteness, we suggest that null that clauses are FinPs, whereas overt that clauses have an extra functional layer above FinP, lexicalizing either the Force head under non-factive predicates or the light demonstrative head d under factive predicates. These three different underlying structures also successfully account for different syntactic patterns found between overt and null that clauses in various contexts.