AbstractThe syntactic parallelism between relative clauses and adverbial clauses in English has led researchers to hypothesize that both types of clauses may share a common derivation process. While Persian relative clauses follow a different derivation pattern from English, the syntactic resemblance between Persian relative and adverbial clauses suggests a uniform derivation process. This study seeks to apply the analysis of relative clauses to adverbial clauses by adopting the most effective available approach to clarify the derivation of Persian relative clauses. One challenge lies in the absence of “-i” in the DP head, and another is the lack of a gap or resumptive pronoun. Findings indicate that the absence of the pronoun in certain temporal and conditional clauses is attributed to relativization within prepositional phrases, allowing for an ellipsis of the entire PP within the clause by analogy with the outer PP, when specific conditions are met. Non-restrictive relative clauses containing “in” (this) represent another category of adverbial clauses resulting from the relativization of an event argument. Given that this element occupies a functional projection, no gap or resumptive pronoun seems to be present. Notably, in this category of adverbial clauses, the DP head is null due to the definiteness of the nominal head. Furthermore, Persian language data validate the proposition that all adverbial clauses are PPs. Unlike English, Persian typically distinctly presents the corresponding preposition and its accompanying noun element.Keywords: Adverbial Clause, Relative Clause, Prepositional Phrase, Adverb, Conjunction Introduction The adverbial clause, a subordinate clause in compound sentences, has not been given due credence in Persian compared to complementary and relative subordinate clauses. In English, the syntactic behavior of relative and adverbial clauses is similar, with central adverbial clauses and relative clauses often exhibiting inconsistency with the main clause phenomena. This inconsistency stems from the derivation of adverbial clauses through the movement of an operator, akin to relative clauses. Local restrictions regarding movement and intervention contribute to this inconsistency. Additional evidence also supports the argument that adverbial clauses are, in fact, free relative clauses.In Persian, although relative clauses and adverbial clauses display similar syntactic behavior, neither is a product of the movement process due to the absence of local restrictions regarding movement and intervention. Karimi (2001) demonstrates that Persian relative clauses result from base generation, where the antecedent (i.e., modified noun) is initially in the specifier of the DP, "-i" occupies the head position, and its complement is a clause: [D CP]. In this structure, the relative operator resides in the specifier of the CP, and a gap or resumptive pronoun, co-indexed with the antecedent and the operator, is produced within the clause.The present research aims to determine whether adverbial clauses can be analyzed similarly, addressing questions such as whether temporal adverbial clauses can be classified as PPs, as proposed by Demirdache and Uribe-Etxebarria (2004), and whether this analysis can be extended to non-temporal adverbial clauses. Materials and MethodsWhen applying Karimi's (2001) analysis to Persian adverbial clauses, two main challenges arise: the absence of "-i" in the head of DP in some adverbial clauses and the lack of a gap or resumptive pronoun in any adverbial clauses. This stands in contrast to the relativization of lower-level nouns (including adjuncts), where the presence of a resumptive pronoun is typically mandatory.To address these challenges, we first examine temporal clauses, considering them as a type of PP based on Demirdache and Uribe-Etxebarria's (2004) perspective. Subsequently, we will explore non-temporal clauses and demonstrate how the restrictiveness of relative clauses impacts the presence or absence of an element co-indexed with the antecedent. This approach provides a rationale for the absence of "-i" in the head of DP in certain adverbial clauses.All Persian examples included in this study were created by the author, and their classification as grammatical or ungrammatical was determined based on the author's intuition. Discussion of Results and ConclusionsIn Example 1, the adverbial clause is regarded as a PP with an omitted P. Within this PP, there is a relative clause complementing the determiner "-i", and the resumptive pronoun is also omitted from this clause. Example 1b illustrates the omitted elements.The tests conducted in this research demonstrate that the rule of "removing the entire PP containing the resumptive pronoun in relative clauses" is applicable when five specific conditions are met:Relativization has occurred for the complement of the preposition.The co-indexed element in the relative clause also serves as the complement of a preposition.The prepositions involved are identical.Both PPs function as adjuncts.The adverbs are limited to time or place expressions.The reason for the aforementioned omission can be attributed to the ease of mentally accessing the deleted element. However, when examining adverbial clauses beginning with phrases such as "be mahz-e in-ke" (as soon as), "be dalile-e in-ke" (because), or "be jay-e in-ke" (instead of), it is not possible to consider such an omission under any circumstances. In these clauses, the antecedent is the demonstrative pronoun "in" (this), and the referent of this pronoun is posterior instead of preceding. The referent of "this" is the event referenced within the clause.This situation mirrors the structure of the so-called "clausal complement of nouns," whose main distinction from relative clauses lies in the absence of a co-indexed element with the antecedent. The clausal complement of nouns is a non-restrictive relative clause, with the antecedent co-indexed to an event argument within the clause. Since this element appears in one of the functional projections, it seems that clausal complements of nouns lack a gap or resumptive pronoun. Consequently, the co-indexed element is present in these clauses, enabling the defense of relativeness in other adverbial clauses containing the demonstrative pronoun "in" (this). These clauses are a form of non-restrictive relative clauses, while temporal adverbial clauses (Example 1) fall under the category of restrictive relative clauses.A characteristic feature of non-restrictive clauses is the absence of "-i" as the head of the main DP. This head is left empty when the antecedent is definite, as written Persian does not utilize a definite article. Consequently, "-i" only appears in the head of DP when dealing with relative clauses whose antecedents are indefinite.According to Demirdache and Uribe-Etxebarria (2004), temporal clauses are PPs that may feature either a null P or a null ZeitP (DP). Interestingly, in Persian, these two elements are prominently present in most adverbial clauses. As a result, not only can Demirdache and Uribe-Etxebarria's claim be substantiated by Persian data, but this analysis can also be extended to non-temporal adverbial clauses. This is because the two elements in question - a preposition and a noun - are typically found in non-temporal Persian clauses, including those pertaining to cause, purpose, opposition, negation, substitution, and condition. It is evident that during the grammaticalization process, some so-called conjunctions have lost their prepositions, some have forfeited their nominal elements, and others have experienced the loss or occasional concealment of both components. Thus, what is referred to as a conjunction actually consists of a preposition alongside its complement, the DP, which contains a relative clause.