A clause can be defined as a fundamental grammatical unit comprising a subject and a predicate (verb phrase).

Subject: Identifies who or what is performing the action or being described.
Predicate (Verb Phrase): Contains the verb and all the elements that depend on it to express a complete idea about the subject.

For example, in the clause:

The children played happily in the park.

Subject: The children (identifies who performed the action)
Predicate (Verb Phrase): played happily in the park (contains the verb "played" and other elements describing how and where the action occurred, providing a complete idea about what the children did).

Clauses can be classified in terms of finiteness:

Feature	Finite Clause	Non-Finite Clause
Verb Form	Finite verb (shows tense and agreement)	Non-finite verb (infinitive, participle, gerund)
Subject	Usually explicit	Often implied or understood, sometimes explicit
Independence	Can stand alone (if main clause)	Cannot stand alone (always subordinate)
Functions	Main clause; Subordinate clause (as noun clause, adj clasue, adv clause)	Nominal (noun-like), Adjectival (adj-like), Adverbial (adv-like)

Subordinating Words and Finite Subordinate Clauses

Subordinate clauses, which cannot stand alone as sentences, are typically introduced by subordinating words. These words help connect the subordinate clause to the main clause and indicate the relationship between the two. Subordinating words can be subordinating conjunctions or relative pronouns/adverbs.

Subordinating Words:

Subordinating Conjunctions: These introduce adverb clauses and show relationships such as time, cause, condition, contrast, etc. Common examples include: because, if, when, while, although, since, before, after, until, unless, as, so that, even though, where, wherever, whether.
- Example: She missed the bus because she was running late.
- Example: If you finish your homework, you can go outside.
- Note: These conjunctions act only as connectors between the clauses. They do not have a grammatical role (like a subject, object, or adverb) within the clause they introduce.
Relative Pronouns: These words (who, whom, whose, which, that) introduce adjective clauses and relate the clause to a noun or pronoun in the main clause.
- Example: The woman who works in the bakery is my neighbor.
- Example: The book that I borrowed is interesting.
Relative Adverbs: These words (where, when, why) also introduce adjective clauses, modifying nouns related to place, time, or reason.
- Example: I remember the day when we first met.
- Example: This is the restaurant where we used to eat.
Interrogative Words (Wh-words): This is a specialized group of words (who, what, where, when, why, how) and phrases (how long, how much, how many, how often) that primarily introduce noun clauses. These clauses act like nouns in the main sentence (for example, as the subject or object of a verb), often embedding an indirect question. While they function as subordinating words by connecting clauses, their key difference is that they also play a grammatical role within their own clause, not just as an outside connector.
- Interrogative Pronouns: These act as pronouns within their clause – either as the subject, object, or possessive.
  - who: Example: She asked who was at the door. ("who" is the subject of "was at the door")
  - whom: Example: I wonder whom he spoke to. ("whom" is the object of "to" within the clause)
  - whose: Example: Do you know whose car this is? ("whose" shows possession for "car" within the clause)
  - what: Example: He couldn't remember what he said. ("what" is the object of "said" within the clause)
  - which: Example: Tell me which book you prefer. ("which" modifies "book" and acts as a pronoun within the clause)
- Interrogative Adverbs: These act as adverbs within their clause, modifying a verb, adjective, or another adverb.
  - when: Example: I need to find out when the store opens. ("when" modifies "opens")
  - where: Example: They can't decide where to go for vacation. ("where" modifies "to go")
  - why: Example: He didn't explain why he left early. ("why" modifies "left")
  - how: Example: Show me how you solved the problem. ("how" modifies "solved")
  - how long: Example: He asked how long it would take. ("how long" modifies "would take")
  - how much: Example: We need to know how much it costs. ("how much" modifies "costs")
  - how many: Example: The teacher asked how many students were present. ("how many" modifies "were present")
  - how often: Example: She wanted to know how often he visited. ("how often" modifies "visited")

Summary of Distinction:

To put it simply:

Subordinating Conjunctions (like because, although, if, unless) are external connectors that primarily introduce adverbial clauses.
Interrogative Words/Wh-words (like who, what, where, when, why, how, how long) are internal participants and connectors that primarily introduce noun clauses. They function as a noun or adverb inside the clause they introduce.

Note:

The name of the clause tells you its function.

If a clause functions as an adverb, we call it an adverbial clause.
If a clause functions as a noun, we call it a noun clause.
If a clause functions as an adjective, we call it an adjective clause.

It's true that some "subordinating words" (like when or where) can introduce different types of clauses depending on how that clause is used in the sentence.

"When" introducing an adverbial clause: "We left when the party ended." (tells when we left)
"When" introducing a noun clause: "I don't know when the party ended." (is the thing I don't know)
"When" introducing an adjective clause: "I remember the day when the party ended." (describes "day")

Function as an adverb vs (Adverb/Adverb phrase/Adverb clause)

"Function as an adverb" (The Job/Role):
- This describes what a word or group of words is doing in a sentence.
- The job of an adverb is to modify (give more information about) a verb, an adjective, or another adverb.
- It answers questions like: When? Where? How? Why? To what extent?
- Examples of the "job":
  - In "He ran quickly," "quickly" is doing the job of telling how he ran.
  - In "She was very happy," "very" is doing the job of telling to what extent she was happy.
(Adverb / Adverb Phrase / Adverb Clause) (The Workers/Types of Units):
- These are the different types of grammatical units that can perform the "function as an adverb." They are classified by their structure.
- a) Adverb (Single Word):
  - This is a single word that performs the adverbial function.
  - Examples: quickly, here, today, very, never
  - Example in action: "He ran quickly." (Single word doing the adverb job)
- b) Adverb Phrase:
  - This is a group of words that does NOT have its own subject and verb.
  - It acts as a single unit to perform the adverbial function.
  - Examples:
    - Prepositional phrase acting as adverb: "They met at the cafe." (tells where they met)
    - Infinitive phrase acting as adverb: "He studies to get good grades." (tells why he studies)
    - Adverb + Modifier(s): "He ran very quickly." (a phrase of adverbs)
  - Example in action: "She sings with great passion." (Phrase doing the adverb job)
- c) Adverb Clause (or Adverbial Clause):
  - This is a group of words that HAS its own subject and verb (making it a clause).
  - It is introduced by a subordinating conjunction (because, when, if, although, etc.).
  - It acts as a single unit to perform the adverbial function.
  - Example in action: "We waited until the sun set." (Clause doing the adverb job)

Functions of Finite Subordinate Clauses:

Finite subordinate clauses, containing a subject and a verb that shows tense and agreement, can function as different parts of speech within a main clause:

Noun Clauses: Function as nouns, acting as subjects, objects, complements, or objects of a preposition.
- Subject: What she said surprised me.
- Object: I know that he is honest.
- Complement: The problem is that we don't have enough time.
- Object of a Preposition: Pay attention to what the speaker is saying.
Adjective (Relative) Clauses: Modify nouns or pronouns, providing additional information.
- Example: The book that I borrowed from the library is interesting.
Adverb Clauses: Modify verbs, adjectives, or adverbs, indicating time, reason, condition, etc.
- Time: When the rain stops, we will go outside.
- Reason: She is happy because she received good news.
- Condition: If you study hard, you will succeed.

Structures of Finite Subordinate Clauses

Non-Finite Clauses

Features

Contain a non-finite verb. A non-finite verb does not show tense and does not agree with the subject.
The subject is often implied or understood from the main clause (explained below)
Cannot stand alone as a complete sentence; they are always dependent on a main clause.
Use one of three non-finite verb forms:
- Infinitives: The base form of the verb, often with "to" (to read, to go).
  - Example: To read many books broadens your mind.
  - Example: She went to the library to study.
- Participles: Can be present participles (verb ending in "-ing," e.g., reading, going) or past participles (often ending in "-ed," "-en," or irregular forms, e.g., read, gone).
  - Example (Present Participle): Reading a book, she relaxed.
  - Example (Past Participle): Forgotten on the shelf, the letter was lost.
- Gerunds: The "-ing" form of the verb used as a noun (reading, going).
  - Example: Reading is a great hobby.
  - Example: She enjoys reading in the park.

Explaining “The subject is often implied or understood from the main clause”

Since non-finite verbs don't have tense or agree with a subject, the subject of the non-finite clause is often omitted when it's the same as the subject or object of the main clause, or when it's clear from the context.

Here's a breakdown with examples for each type of non-finite clause:

1. Infinitive Clauses:

Subject implied when the subject of the main clause is the same:
- Example: She wants to go home. Here, the subject of the main clause is "She." The implied subject of the infinitive clause "to go home" is also "She." We understand it as "She wants herself to go home," but "herself" is not explicitly stated.
- Example: They decided to leave early. The subject of the main clause is "They." The implied subject of "to leave early" is also "They."
Subject implied when the object of the main clause becomes the subject of the infinitive action:
- Example: He asked her to help him. The object of the main verb "asked" is "her." She is the one who is doing the helping, so "her" is the implied subject of the infinitive clause "to help him."
- Example: The teacher told the students to be quiet. The object of "told" is "the students," and they are the ones who need to be quiet. "The students" is the implied subject of "to be quiet."
Subject explicitly stated (often with "for"): Sometimes, the subject of the infinitive clause is different from the main clause and is introduced by "for."
- Example: It is important for the students to study. Here, "the students" is the explicit subject of the infinitive clause "to study," and it's different from the implied subject "it" of the main clause.
- Example: She waited for the rain to stop. "The rain" is the explicit subject of "to stop."

2. Participle Clauses (Present and Past):

Subject implied when it's the same as the subject of the main clause:
- Example (Present Participle): Walking down the street, she saw a familiar face. The subject of the main clause is "she." The implied subject of the participle clause "Walking down the street" is also "she" (i.e., She was walking down the street).
- Example (Past Participle): Forgotten in the drawer, the letter was never sent. The subject of the main clause is "the letter." The implied subject of the participle clause "Forgotten in the drawer" is also "the letter" (i.e., The letter was forgotten in the drawer).
Subject explicitly stated (though less common at the beginning of the clause): Sometimes, the subject is made explicit, often with a possessive pronoun or noun. These are sometimes called "absolute constructions."
- Example (Present Participle): The rain having stopped, we went outside. Here, "the rain" is the explicit subject of the participle clause "having stopped."
- Example (Past Participle): His work completed, he went home. "His work" is the explicit subject of "completed."

3. Gerund Clauses:

Subject often implied when it's the same as the subject of the main clause or when it's general:
- Example: Swimming is good exercise. Here, the subject of the gerund clause "Swimming" is general – it refers to the activity itself, not a specific person.
- Example: She enjoys reading in the park. The subject of the main clause is "She," and the implied subject of the gerund phrase "reading in the park" is also "She" (i.e., Her reading in the park).
Subject explicitly stated (often with a possessive): When the actor of the gerund needs to be clear and is different from the main clause subject, a possessive noun or pronoun is often used.
- Example: His constant complaining annoyed everyone. "His" explicitly shows who is doing the complaining.
- Example: The teacher didn't like John's talking during the lesson. "John's" clearly indicates who was talking.

Functions of Non-Finite Clauses:

Non-finite clauses, lacking tense and subject agreement, have different but equally important functions:

Nominal Functions (acting like nouns):
- Subject: Swimming in the ocean is exhilarating. (Gerund clause)
- Object of a Verb: She enjoys reading novels. (Gerund clause)
- Complement: His ambition is to become a pilot. (Infinitive clause)
- Object of a Preposition: He is good at solving puzzles. (Gerund clause)
Adjectival Functions (acting like adjectives):
- Post-modifier of a Noun: The man sitting in the corner is my uncle. (Present participle clause)
- Post-modifier of a Noun: The letter written last week arrived today. (Past participle clause)
- Reduced Relative Clauses: The car parked outside is mine. (Past participle clause, reduced from "that is parked outside")
Adverbial Functions (acting like adverbs):
- Time: Having finished work, she went home. (Perfect participle clause)
- Reason: Being tired, I went to bed early. (Present participle clause)
- Purpose: He went to the store to buy groceries. (Infinitive clause)
- Manner: She looked at him smiling sweetly. (Present participle clause)
- Condition: Provided that you study, you will pass. (Past participle clause in a conditional structure)

Clauses