What part of speech is the word subject

In grammar, the sentence is the simplest unit which can express a complete thought independently. It is written with a capital letter, an end punctuation (a period, an exclamation point, or a question mark), and most importantly, it has a subject and a predicate. In this article, one of the most important parts of a sentence will be explored—the subject.

What is the Subject and its Function?

In its simplest sense, the subject refers to the doer of the action or to what (or whom) the sentence is all about. It can either be a person, a place, a thing, or an idea, and can come in the form of a noun or a pronoun. Take a look at the examples below:

• During the exam, Tommy slept in his chair.
• In this example, the verb is “slept” and the doer of the action is the noun “Tommy,” which is why he is the subject in this sentence.

• They are extremely wealthy.
• The italicized verb in this example expresses the state of being of the pronoun “they,” which is the subject in the sentence.

• Joey and Phoebe went to the audition.
• In this sample sentence, “Joey” and “Phoebe” are both the doers of the action “went.” Therefore, both of them are the subjects in this example.

What are the Different Forms of Subjects?

Listed below are some of the most important terms related to the concept of the subject.

1. Complete Subject

The complete subject simply refers to:

Examples:

• The muscular man lifted the heavy table and transferred it to the other room.
• In this example, the doer of the italicized verbs “lifted” and “transferred” is the “man.” But if you’re asked to underline the complete subject, you must also include the descriptive words (modifiers): “the” and “muscular.” Therefore, the complete subject in this sentence is the whole underlined part.

• The tall and pretty lady fell into the freezing water.
• In this sentence, the complete subject is “the tall and pretty lady,” because “lady” is the one who did the action “fell”. Take note that the words before the word “lady” are just the modifiers or descriptive words that distinguish this lady (in the sentence) from the other ladies.

2. Simple Subject

Basically, the simple subject refers to the noun or pronoun which is being or doing something. Unlike the complete subject, this doesn’t require you to include the descriptive words (modifiers)—just the main noun or pronoun will do.

Examples:

• The mighty superhero saved the day.
• The simple subject in this sentence is the noun “superhero,” because he is the doer of the action “saved”.

• She is indeed the epitome of kindness.
• The simple subject is the pronoun “she,” because it refers to the person being talked about in this sentence.

3. Compound Subject

This term simply refers to two or more subjects in a single sentence joined together by a connector.

Examples:

• The captain and his ship were lost in the heavy storm.
• The underlined part is the compound subject consisting of the two main nouns, “captain” and “ship,” plus the connector “and.” This is considered as the compound subject because the captain and his ship were the ones who “were lost,” or simply the doers of the action word or verb.

• Christmas and New Year are my favorite holidays.
• This sample sentence is about two events namely, “Christmas” and “New Year.” Therefore, these two nouns connected by the word “and” are considered as the compound subject in this sentence.

What is the Easiest Way to Spot the Subject in the Sentence?

If you are having difficulties figuring out what is the subject in a sentence, an easy tip to remember is to identify the verb first. (Note: A verb refers to a word which expresses an action or a state of being.)

Once you have identified the verb, the next thing you should do is ask the question “what” or “who” is doing this?
For example:

• Billy jumped over the fence to escape the dog.
• Step 1- Ask “What is the verb?”
• The verb is the action word “jumped.”
• Step 2- Ask ”Who jumped?” or “What jumped?”
• Since “Billy” jumped, he is the subject in the sentence.

From the simple steps mentioned, you will be able to identify the subject without even breaking a sweat. Also, you must know that there are times when the subject is not explicitly stated or is not actually written in the sentence, such as in the examples below:

1. Run!
2. Please read the instructions carefully.

In sentences like those above, which state a command or a request, it is understood that the subject who does the italicized action words is “you.”

Final Thoughts

A deep understanding of the subject is very important for you to be able to form well-written compositions. This is one of the most basic and fundamental concepts in grammar, so you really have to get a good grasp on this topic before advancing to more complicated ones. With the simple explanations, examples, and tips provided in this article, studying this area shouldn’t be that hard at all.

The subject in a simple English sentence such as John runs, John is a teacher, or John drives a car, is the person or thing about whom the statement is made, in this case John. Traditionally the subject is the word or phrase which controls the verb in the clause, that is to say with which the verb agrees (John is but John and Mary are). If there is no verb, as in Nicola – what an idiot!, or if the verb has a different subject, as in John – I can’t stand him!, then ‘John’ is not considered to be the grammatical subject, but can be described as the topic of the sentence.

While these definitions apply to simple English sentences, defining the subject is more difficult in more complex sentences and in languages other than English. For example, in the sentence It is difficult to learn French, the subject seems to be the word it, and yet arguably^{[according to whom?]} the real subject (the thing that is difficult) is to learn French. A sentence such as It was John who broke the window is more complex still. Sentences beginning with a locative phrase, such as There is a problem, isn’t there?, in which the tag question isn’t there? seems to imply that the subject is the adverb there, also create difficulties for the definition of subject.^[1]

In languages such as Latin and German the subject of a verb has a form which is known as the nominative case: for example, the form ‘he’ (not ‘him’ or ‘his’) is used in sentences such as he ran, he broke the window, he is a teacher, he was hit by a motorist. But there are some languages such as Basque or Greenlandic, in which the form of a noun or pronoun when the verb is intransitive (he ran) is different from when the verb is transitive (he broke the window). In these languages, which are known as ergative languages, the concept of subject may not apply at all.

Technical definition[edit]

The subject (glossing abbreviations: SUB or SU) is, according to a tradition that can be traced back to Aristotle (and that is associated with phrase structure grammars), one of the two main constituents of a clause, the other constituent being the predicate, whereby the predicate says something about the subject.^[2][3] According to a tradition associated with predicate logic and dependency grammars, the subject is the most prominent overt argument of the predicate. By this position all languages with arguments have subjects, though there is no way to define this consistently for all languages.^[4] Even in languages such as English, there is not always a perfect match between the semantic predicand and the subject, as a predicate may be predicated on an argument in another clause (see raising).

From a functional perspective, a subject is a phrase that conflates nominative case with the topic. Many languages (such as those with ergative or Austronesian alignment) do not do this, and by this definition would not have subjects.

All of these positions see the subject in English determining person and number agreement on the finite verb, as exemplified by the difference in verb forms between he eats and they eat. The stereotypical subject immediately precedes the finite verb in declarative sentences in English and represents an agent or a theme. The subject is often a multi-word constituent and should be distinguished from parts of speech, which, roughly, classify words within constituents.

In the example sentences below, the subjects are indicated in boldface.

1. The dictionary helps me find words.
2. Strangely enough, ice cream appeared on the table.
3. The man who is sitting over there told me that he just bought a ticket to Tahiti.
4. Nothing else is good enough.
5. That nothing else is good enough shouldn’t come as a surprise.
6. To eat six different kinds of vegetables a day is healthy.
7. Despite her objections, he sold us ten bags of clothes.

Forms of the subject[edit]

The subject is a constituent that can be realized in numerous forms in English and other languages, many of which are listed in the following table:

Noun (phrase) or pronoun	The large car stopped outside our house.
A gerund (phrase)	His constant hammering was annoying.
A to-infinitive (phrase)	To read is easier than to write.
A full that-clause	That he had traveled the world was known to everyone.
A free relative clause	Whatever he did was always of interest.
A direct quotation	I love you is often heard these days.
Zero (but implied) subject	Take out the trash!
An expletive	It is raining.
A cataphoric it	It was known to everyone that he had traveled the world.
A preposition phrase	After lunch is too late.

Criteria for identifying subjects[edit]

There are several criteria for identifying subjects:^[5]

1. Subject-verb agreement: The subject agrees with the finite verb in person and number, e.g. I am vs. *I is.^[6]
2. Position occupied: The subject typically immediately precedes the finite verb in declarative clauses in English, e.g. Tom laughs.
3. Semantic role: A typical subject in the active voice is an agent or theme, i.e. it performs the action expressed by the verb or when it is a theme, it receives a property assigned to it by the predicate.

Of these three criteria, the first one (agreement) is the most reliable. The subject in English and many other languages agrees with the finite verb in person and number (and sometimes in gender as well). The second and third criterion are merely strong tendencies that can be flouted in certain constructions, e.g.

1. Tom is studying chemistry. — The three criteria agree identifying Tom as the subject.
2. Is Tom studying chemistry? — The 1st and the 3rd criteria identify Tom as the subject.
3. Chemistry is being studied (by Tom). — The 1st and the 2nd criteria identify Chemistry as the subject.

In the first sentence, all three criteria combine to identify Tom as the subject. In the second sentence, which involves the subject-auxiliary inversion of a yes/no-question, the subject immediately follows the finite verb (instead of immediately preceding it), which means the second criterion is flouted. And in the third sentence expressed in the passive voice, the 1st and the 2nd criterion combine to identify chemistry as the subject, whereas the third criterion suggests that by Tom should be the subject because Tom is an agent.

The fourth criterion is better applicable to languages other than English given that English largely lacks morphological case marking, the exception being the subject and object forms of pronouns, I/me, he/him, she/her, they/them.

The fifth criterion is helpful in languages that typically drop pronominal subjects, such as Spanish, Portuguese, Italian, Latin, Greek, Japanese, and Mandarin. Though most of these languages are rich in verb forms for determining the person and number of the subject, Japanese and Mandarin have no such forms at all. This dropping pattern does not automatically make a language a pro-drop language. In other languages, like English and French, most clauses should have a subject, which should be either a noun (phrase), a pronoun, or a clause. This is also true when the clause has no element to be represented by it. This is why verbs like rain must have a subject such as it, even if nothing is actually being represented by it. In this case, it is an expletive and a dummy pronoun. In imperative clauses, most languages elide the subject, even in English which typically requires a subject to be present, e.g.

• Give it to me.
• Dā mihi istud. (Latin)
• Me dá isso. (Brazilian Portuguese)
• Dá-me isso. (European Portuguese)
• Dámelo. (Spanish)
• Dammelo. (Italian)

Coordinated sentences[edit]

One criterion for identifying a subject in various languages is the possibility of its omission in coordinated sentences such as the following:^[7] The man hit the woman and [the man] came here.

In a passive construction, the patient becomes the subject by this criterion: The woman was hit by the man and [the woman] came here.

In ergative languages such as the nearly extinct Australian language Dyirbal, in a transitive sentence it is the patient rather than the agent that can be omitted in such sentences: Balan d^yugumbil baŋgul yaraŋgu balgan, banin^yu ‘The man (bayi yara) hit the woman (balan d^yugumbil) and [she] came here’

This suggests that in ergative languages of this kind the patient is actually the subject in a transitive sentence.

Difficult cases[edit]

There are certain constructions that challenge the criteria just introduced for identifying subjects. The following subsections briefly illustrate three such cases in English: 1) existential there-constructions, 2) inverse copular constructions, and 3) locative inversion constructions.

Existential there-constructions[edit]

Existential there-constructions allow for varying interpretations about what should count as the subject, e.g.

1. There’s problems.
2. There are problems.

In sentence 1, the first criterion (agreement) and the second criterion (position occupied) suggest that there is the subject, whereas the third criterion (semantic role) suggests rather that problems is the subject. In sentence 2, in contrast, agreement and semantic role suggest that problems is the subject, whereas position occupied suggests that there is the subject. In such cases then, one can take the first criterion as the most telling; the subject should agree with the finite verb.^[8]

Inverse copular constructions[edit]

Another difficult case for identifying the subject is the so-called inverse copular construction, e.g.^[9]

1. The boys are a chaotic force around here.
2. A chaotic force around here is the boys. — Inverse copular construction

The criteria combine to identify the boys as the subject in sentence 1. But if that is the case, then one might argue that the boys is also the subject in the similar sentence 2, even though two of the criteria (agreement and position occupied) suggest that a chaotic force around here is the subject. When confronted with such data, one has to make a decision that is less than fully arbitrary. If one assumes again that criterion one (agreement) is the most reliable, one can usually identify a subject.

Locative inversion constructions[edit]

Yet another type of construction that challenges the subject concept is locative inversion, e.g.

1. Spiders have been breeding under the bed.
2. Under the bed have been breeding spiders. — Locative inversion
3. *Where have been breeding spiders? — Failed attempt to question the location
4. Where have spiders been breeding? — Successful attempt to question the location

The criteria easily identify spiders as the subject in sentence 1. In sentence 2, however, the position occupied suggests that under the bed should be construed as the subject, whereas agreement and semantic role continue to identify spiders as the subject. This is so despite the fact that spiders in sentence 2 appears after the string of verbs in the canonical position of an object. The fact that sentence 3 is bad but sentence 4 is good reveals that something unusual is indeed afoot, since the attempt to question the location fails if the subject does not immediately follow the finite verb. This further observation speaks against taking spiders as the subject in sentence 2. But if spiders is not the subject, then the sentence must lack a subject entirely, which is not supposed to be possible in English.

Subject-less clauses[edit]

The existence of subject-less clauses can be construed as particularly problematic for theories of sentence structure that build on the binary subject-predicate division. A simple sentence is defined as the combination of a subject and a predicate, but if no subject is present, how can one have a sentence? Subject-less clauses are absent from English for the most part, but they are not unusual in related languages. In German, for instance, impersonal passive clauses can lack a recognizable subject, e.g.

The word gestern ‘yesterday’ is generally construed as an adverb, which means it cannot be taken as the subject in this sentence. Certain verbs in German also require a dative or accusative object instead of a nominative subject, e.g.

Since subjects are typically marked by the nominative case in German (the fourth criterion above), one can argue that this sentence lacks a subject, for the relevant verb argument appears in the dative case, not in the nominative.

Impersonal sentences in Scottish Gaelic can occasionally have a very similar form to the first German example where an actor is omitted. In the following sentence, the word ‘chaidh’ («went») is an auxiliary carrying tense and is used in an impersonal or passive constructions. The word ‘falbh’ («leaving») is a verbal noun.

Subjects in sentence structure[edit]

The subject receives a privileged status in theories of sentence structure. In those approaches that acknowledge the binary division of the clause into a subject and a predicate (as is the case in most phrase structure grammars), the subject is usually an immediate dependent of the root node, whereby its sister is the predicate. The object, in contrast, appears lower in the structure as a dependent of the/a verb, e.g.^[10]

Subjects are indicated using blue, and objects using orange. The special status of the subject is visible insofar as the subject is higher in the tree each time than the object. In theories of syntax that reject the initial division (as is the case in most dependency grammars), the subject is nevertheless also granted a privileged status insofar as it is an immediate dependent of the finite verb. The following trees are those of a dependency grammar:^[11]

The subject is a dependent of the root node, the finite verb, in both trees. The object, in contrast, appears lower in the second tree, where it is a dependent of the non-finite verb. The subject remains a dependent finite verb when subject-auxiliary inversion occurs:

The prominence of the subject is consistently reflected in its position in the tree as an immediate dependent of the root word, the finite verb.

See also[edit]

• Complement (linguistics)
• Copula
• Grammatical case
• Object (grammar)
• Preparatory subject
• Quirky subject
• Sentence (linguistics)
• Subjective (grammar)

Notes[edit]

References[edit]

The subject in an English sentence

In order to have a complete sentence, each sentence must have a subject and a verb. These two parts of speech are the fundamental part of the subject and predicate that make up a sentence. Every sentence has a subject and a predicate, or it is not considered a complete sentence.

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What is a Subject?

A subject is the person or thing that is doing an action, or the person or thing that is the focus of the sentence. Most of the time the subject comes at the beginning of a sentence, in which case it is very easy to identify. Take the example below:

• Mary likes to run at the public park.

In this case, the person who is doing the action (liking to run) is Mary. Mary is the subject. This is still the case when you have two nouns. If someone is doing something to someone else, it can get confusing. However, the same principle applies. If the person or thing is the cause of the action, they are the subject:

• My brother throws him the ball.

For this sentence, the person who is throwing is my brother. As a side note, the other nouns are both objects. They have the action done to them. Him is the indirect object, and the ball is the direct object.

Subjects Examples in Command

Sometimes, the subject of the sentence is not as clear. This is especially the case when you have a command like the one below:

• Do your homework!

In this case, the subject of the sentence is not clear. There is no obvious person or thing doing their homework. However, for most commands, the subject is implied, rather than directly mentioned. Most of the time the subject is the implied you. This concept is known as the you understood idea.

Subjects Examples in Passive Voice

The passive voice is present in sentences that passively tell an action. Usually, it has the word by in it, and the person or thing doing the action is at the end of the sentence rather than at the beginning.

This is confusing for several reasons. First, the actor is not always included in the sentence. Second, it is the thing that has been acted upon that is the subject. Take this example:

• The newspaper article was written by the journalist.

In this case, the person who did the action is the journalist. However, because of the structure of the sentence, the newspaper article is the subject. You can identify the subject by asking who or what the verb agrees with.

Or, you can pretend that the actor in the sentence is not written. In that case, the linking verb (am, is, are, was, were, be, being, been) is the action. The first noun is the subject because they do the action of “being” something. Take this example:

• The newspaper article was written.

In this sentence, the person who wrote the article is unclear. We know from context it is likely a journalist, but the sentence itself does not mention anything. In addition, the sentence is not a command. There is no implied “you” in the subject. However, it is a complete sentence. For this type of sentence, the thing or person that is, is the subject.

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What is a Predicate?

The predicate of the sentence is the part that contains the action. It is the part of the sentence that is not the subject, and includes all the descriptions of the action and the objects that are affected by the action. Take this example:

• Mary likes to run at the public park.

The question you can ask yourself here is, “What does Mary do”? The answer, likes to run at the public park, is the predicate. Notice that the predicate includes the verb in the sentence (likes) and all the rest of the words that describes what she likes.

When you have multiple nouns, the concept is the same. The entirety of the sentence that excludes the subject is the predicate. If the sentence has objects, either direct or indirect, they are part of the predicate.

• My brother throws him the ball.

In this sentence, throws him the ball is the predicate.

Predicates Examples in Command

In a command sentence, the entirety of the sentence is usually the predicate.

• Do your homework!

For this example, do your homework is the predicate. The subject, the implied you, has no influence on the rest of the sentence.

Predicates Examples in Passive Voice

The same principle that governs how to find the subject of a passive voice sentence applies here. When you understand the meaning of the sentence, the actor can be quite clear. However, that is not usually the subject. Refer again to the sentence below:

• The newspaper article was written by the journalist.

As with the explanation above, the subject is the noun that the verb agrees with. They do the action in the sentence, by “being” something. In this case, the newspaper article was written by the journalist.

The bolded part of the sentence is the predicate. It shows what the newspaper was, and includes the phrases that describe being written (by the journalist).

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Simple Subjects and Predicates

When categorizing subjects and predicates, you have two options. They can either be simple or compound. The different is evident when you analyze the subjects or predicates separately.

Simple subjects are subjects that have only one actor. Usually this means the subject does not have the word and. It does not matter what they do, just that there is only one. See the following examples. The words in the parentheses after the sentences are the simple subjects:

1. The snowman, friend to all the children, melts in the snow. (the snowman, friend to all the children; even though there seems to be more than one noun, the second phrase acts like an adjective and describes the singular subject, snowman)
2. Amber likes to write her own stories and draw her own pictures. (Amber)
3. Go to your room! (You)
4. The policy was proposed and passed by the Congress of legislators and the president. (the policy)

When the subject does only one thing (or is only one thing), that is a simple predicate. Most of the time, this means that there is only one verb. As a result, simple predicates usually do not have the word and, or only have and as part of a modifying adverb. See the following examples (the predicates are in parentheses):

1. The water bottle sat on the table. (sat on the table)
2. Gordon and Anna went to the library. (went to the library)
3. Finish washing the dishes! (finish washing the dishes)
4. The newspapers and websites all were screened by the government’s propaganda department. (were screened by the government’s propaganda department)

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Compound Subjects and Predicates

As a contrast to simple subjects and predicates, compound subjects and predicates are those that have either two people or things doing an action, or two actions that are performed. If you can see an “and” in the subject or predicate, that usually means it is compound.

The compound subjects have two or more people and things doing an action. The trick to understand here is that the two or more people does not include nouns that are plural.

For example, a sentence where the parents are taking the children to school does not have a compound subject. There are usually two parents, but grammatically, they are represented by one word. It is the same thing with a phrase like a herd of elephants, which represents lots of animals but grammatically is only one herd.

By contrast, if you have Amy’s and Timmy’s parents, that is a compound subject. Even if Amy and Timmy are siblings, you could break the phrase into Amy’s parents and Timmy’s parents, so that represents two subjects.

1. The children’s books and backpacks were stolen while they were at lunch. (children’s book and backpacks)
2. The zoo and ice cream store were the favorite destinations of Todd and Sally. (the zoo and ice cream store)

Compound predicates are similar. They need to include two different actions (two verbs) that the subject or subjects do. See the examples below:

1. The water bottle had water and sat on the table. (had water and sat on the table)
2. Gordon and Anna went to the library and read. (went to the library and read)
3. Finish washing the dishes and put them back! (finish washing the dishes and put them back)
4. The newspapers and websites all were screened and approved by the government’s propaganda. (were screened and approved by the government’s propaganda)

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Test Yourself

Do you understand the difference between subjects and predicates, simple and compound? Try your hand at the ten questions below. The answers are included at the bottom of the post.

1. Amy and her brother were sick.
2. I was told that this would not be a problem.
3. There are two kinds of wine available, red and white.
4. The teacher and her assistant told the student and his parents that there would be a quiz next class.
5. You and your brother go to your room right now!
6. Don’t you need to pay for that first?
7. Kevin talked to his teacher and thanked her for her help.
8. I like potatoes.
9. Brian was escorted out of the hospital with his parents.
10. Brian and his siblings were escorted out of the hospital.

Check below for the answers!

Answers to Test Yourself

1. Amy and her brother were sick.

Subject: compound (Amy and her brother)

Predicate: simple (were sick)

1. I was told that this would not be a problem.

Subject: simple (I)

Predicate: simple (was told that this would not be a problem)

1. There are two kinds of wine available, red and white.

Subject: simple (two kinds of wine)

Predicate: simple (available)

1. The teacher and her assistant told the student and his parents that there would be a quiz next class.

Subject: compound (the teacher and her assistant)

Predicate: simple (told the student and his parents that there would be a quiz next class). In this case, the student and his parents are both objects of the verb told.

1. You and your brother go to your room right now!

Subject: compound (you and your brother). This is a command, but it clearly is addressing more than one person. That makes it a compound subject.

Predicate: simple (go to your room right now)

1. Don’t you need to pay for that first?

With this and any other question, the easiest way to identify the sentence parts is to rearrange the words. Make the sentence more like a statement. In this case, You don’t need to pay for that first.

Subject: simple (you)

Predicate: simple (don’t need to pay for that first)

1. Kevin talked to his teacher and thanked her for her help.

Subject: simple (Kevin)

Predicate: compound (talked to his teacher and thanked her for her help). The verbs are split in this sentence, but there are still two actions that Kevin did.

1. I like potatoes.

Subject: simple (I)

Predicate: simple (like potatoes)

1. Brian was escorted out of the hospital with his parents.

Subject: simple (Brian). Even though Brian was with his parents, the word with makes the phrase with his parents a prepositional phrase, not part of the subject.

Predicate: simple (was escorted out of the hospital with his parents)

1. Brian and his siblings were escorted out of the hospital.

Subject: compound (Brian and his siblings)

Predicate: simple (were escorted out of the hospital)

Subject and Predicate Worksheets

For more practice on identifying subjects and predicates, check the example worksheets below!

http://www.k12reader.com/verbs/Subject_and_Predicate.pdf

https://www.superteacherworksheets.com/subjectpredicate.html

http://www.teach-nology.com/worksheets/language_arts/subpred/

http://printableworksheets.in/?dq=Complete%20Subject%20And%20Predicate

https://www.education.com/worksheet/article/subject-predicate-two-parts-third/

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The subject is normally a noun or a pronoun.

However, it may also be the infinitive or the gerund form of a verb, or a clause.

«John was happy.» (John is the subject).

«To travel to Europe is always fun.» (To travel is the subject)

«Riding in his car made John happy.» (Riding is the subject)

Interrogative and indefinite pronouns can represent subjects using a linking verb.

«What was his answer?» (subject is answer)

«There are no solutions.» (subject is solutions)

«It was a dark and stormy night.» (subject pronoun it)

«That we tried is what is important.» (subject pronoun that)

Imperative sentences have an understood subject, which is you.

«Clean up the room» (you should clean up the room now)

The subject of a sentence is the key and primary ‘thing’ that the writer/talker is writing/speaking about. In grammar, the word ‘subject‘ refers to the person or thing that performs the action described by the verb.

For example, in the sentence «The cat sat on the mat», the verb is ‘sat.’

So what thing performed the action of sitting? It was the cat.

So ‘cat’ is the subject in this sentence.

The complete subject of a sentence can be a noun phrase, meaning a phrase whose head word is a noun. The subjects in the following examples are enclosed between square brackets with the head noun italicized:

• [The new student] asked a question.
• [A question] was asked.
• [A student who studies linguistics] asked a question.
• Are [your students] enjoying the course?
• [He] thought that [the student] was very clever. (Here ‘he’ is the subject of the main clause and ‘the student’ is the subject of the embedded clause.)
• [I] expected [him] to go. (Here ‘I’ is the subject of the main clause and ‘him’ is the subject of the embedded clause ‘him to go’.)

Various types of clauses can also function as the subject of a sentence when the main verb is a form of ‘to be’:

• [Playing cricket] is fun.
• [That I am alive] is obvious.
• [To leave now] would be a disaster.

Any kind of quoted text can also function as a subject when the verb is a form of ‘to be’:

• [«All work and no play»] was repeated on every page of the manuscript.

The part of speech that should be the subject of a sentence is a noun.
The subject of a sentence is usually a noun or a noun phrase.

Nouns, pronouns, and verbs can serve as subjects.

(noun) The dog ate the cake.

(pronoun) She died after the meal.

(verb, gerund) Eating the cake led to her death.

(verb, infinitive) To eat the cake was a risky move.

For verbs, present participles (often defined as gerunds) or infinitives serve as subjects. (The Critical Reader chooses to specify these in their answer for «What parts of speech can be subjects?») The colloquial explanation, represented in places like ThoughtCo, is that the gerund or infinitive is a verb that serves as a noun phrase, which allows it in turn to serve as a subject.

Other parts of speech are trickier. In general, the words will serve as a noun or noun phrase, most likely due to a process of nominalization or due to an implied noun phrase serving as subject. Note: you want to be deliberate about what you are doing and how the nominalization will be understood; you cannot slap any adjective at the start of any verb and say, «That’s my subject.»

First, implied noun phrases. Take these examples:

(adjective) Slow and steady wins the race. (Source: idiom)

(adjective) Rare is fine. (Source: Cowboy’s Mail Order Bride)

These adjectives have an implied noun phrase that is the subject; they have entered such wide usage that the noun need not be specified. (Examples: slow and steady pacing OR slow and steady action; rare steak.) Context or idiomatic usage suggests how the adjective should be understood.

There are also adjectives and (occasionally) other parts of speech that can be nominalized, or made into nouns:

(nominal adjective / adjective turned into noun) The rich get richer and the poor get poorer.

(nominalized preposition) For is used to specify who will receive the gift card.

Usually these forms are treated as nouns.

Finally, and especially with linking verbs, it is possible to move the grammatical subject to the end of the sentence.

Red is the color of my car.

The subject has been moved to the back of the sentence, and another element has been moved to the front (ThoughtCo gives many examples of subject inversion and fronting). The subject is still the color of my car.