Verbs are the most important part of speech for communication. While every part of speech has an important and unique role, a sentence can be stripped down to just one verb and one subject (which could be a noun, a pronoun, or, in special situations, another verb). But what is a verb? Here's a simple definition:

A verb is an action, occurrance, or state of existence.

But verbs are anything but simple. Verbs can be classified in two general categories: dynamic verbs (also known as lexical verbs), which show physical actions, and static verbs, which show states of existence.

There are three types of static verbs:

• Stative verbs (also called mental action verbs) show how a subject senses, perceives, understands, possesses, or feels about an object (Michael loves music; I feel dizzy). Like dynamic verbs, stative verbs have valency and take objects as complements.
• Linking verbs (also called copula verbs) show how a subject exists by linking the subject with a predicative (She is the student body president). They can also indicate how a speaker senses, perceives, understands, possesses, or feels about a subject (She seems odd). They can also indicate a shift in existence where a subject transforms into something else (Summer becomes fall). The most common linking verbs are the eight forms of "to be" (AKA, the Hamlet verbs): is, was, were, am, are, be, been, being.¹
• Helping verbs (also called auxiliary verbs) are used to clarify the state of how an action exists, whether it is a dynamic action or a static action. These states are known as tense, aspect, and mood.

Verbs can even be more than one word. A phrasal verb is a combination of a verb with an adjective or preposition to create a new verb.

• Don't throw away your shot!
• Go ahead and stand up to them.
• I may just sit around and play video games.

There are even some dynamic verbs that also simultaneously take over functions of other parts of speech in a sentence—these verbals include gerunds (continuous verbs that take the place of a noun), infinitives (uninflected verbs that take the place of a noun or modifier), and participles (perfect and continuous verbs that act as modifiers).

So... verbs are actually pretty complicated.

Since verbs are the most used part of speech in the English language, they are the most diverse and complex. English grammarians have even created a more exacting definition of what constitutes a verb to reflect its complexity: a verb is an act, intentional or ontological, that conveys tense, aspect, valency, and mood.

The rest of this article will look at verb conjugation, which is how the main verb of a clause is selected or changed to

• agree with the person and number of its subject,
• support the type and number of its arguments (valency), and
• define the tense, aspect, and mood of the sentence

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The specific classification and use of helping verbs, as well as the function of verbals, have been sectioned off into other articles.

Helping verbs

Helping verbs

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NUMBER AND PERSON: shows the actor

Verbs are actions, and an action is something (an actor) doing something (behaving or existing in a certain way). Since actions are defined by the actor, they take on qualities of that actor; thus, their grammatical qualities must match to make logical sense. This is called subject-verb agreement.

What are these qualities in nouns or pronouns that a verb needs to match? First is case: the verb only needs to match the noun or pronoun acting as the subject (at least for subject-verb agreement). Next is number: some nouns and pronouns are singular, some are plural, and the correct verb indicates that. Pronouns also indicate person, which is the identity of the subject in relation to the speaker of the sentence.

Here are the guidelines for subject-verb agreement:

SINGULAR NOUNS PAIR WITH PLURAL VERBS

DYNAMIC VERBS: Byron laughs; the dog eats

STATIVE VERBS: Byron believes her; the dog hears something

LINKING VERBS: Byron turns eighteen; the dog smells nice

...except for Hamlet verbs, which must be SINGULAR

HAMLET VERBS: Byron is a clown; the dog was hungry

FIRST- OR SECOND-PERSON PERSONAL PRONOUNS:

ALWAYS PAIR WITH SINGULAR VERB

DYNAMIC VERBS: I laugh; we dance; you eat

STATIVE VERBS: I believe her; we hear something
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LINKING VERBS: we turn eighteen; you smell nice

...except for Hamlets: I PAIRS WITH SINGULAR VERB

I am a clown; I was hungry

ALL OTHERS PAIR WITH PLURAL HAMLET VERBS

we are clowns; you were hungry

THIRD PERSON PLURAL PRONOUNS:

ALWAYS PAIR WITH A SINGULAR VERB

DYNAMIC VERBS: they laugh; they dance; they eat

STATIVE VERBS: they believe her; they love Prince; they hear something
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NON-HAMLET LINKING VERBS: they turn eighteen; they smell nice; they look delicious

...except for Hamlet verbs, which must be PLURAL

HAMLET VERBS: they are clowns; they were hungry

PLURAL NOUNS PAIR WITH SINGULAR VERBS

DYNAMIC VERBS: our boys laugh; the dogs eat

STATIVE VERBS: our boys believe her; the dogs hear something

LINKING VERBS: our boys turn eighteen; the dogs smell nice

...except for Hamlet verbs, which must be PLURAL

HAMLET VERBS: the boys are clowns; the dogs were hungry

THIRD-PERSON SINGULAR PRONOUNS:

​ALWAYS PAIR WITH A PLURAL VERB

DYNAMIC VERBS: he laughs; she dances; it eats

STATIVE VERBS: he believes her; she loves Prince
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LINKING VERBS: he turns eighteen; she smells nice

...except for Hamlet verbs, which must be SINGULAR

HAMLET VERBS: he is a clown; she was hungry
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INDEFINITE PRONOUNS:

​ALWAYS TREAT THEM AS SINGULAR

DYNAMIC VERBS: everyone laughs; nobody eats

STATIVE VERBS: everyone believes her; nobody hears something
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LINKING VERBS: everyone turns eighteen; nobody smells nice

HAMLET VERBS: nobody is a clown; everyone was hungry

CASES WHERE THE SUBJECT ISN'T CLEARLY SINGULAR OR PLURAL:

TREAT TWO SUBJECTS CONNECTED BY AND AS A PLURAL SUBJECT: 
Byron and I laugh; Ann and the boys believe her; the boys and girls smell nice; he and Steve are hungry

FOR TWO SUBJECTS CONNECTED BY OR/NOR, BASE AGREEMENT OFF THE LAST SUBJECT: 
DYNAMIC VERBS: neither the pens nor the pencil writes; neither the pencil nor the pens write
STATIVE VERBS: either the boys or Byron needs help; either Byron or the boys need help
NON-HAMLET LINKING VERBS: neither the cakes nor the sauce looks fresh; neither the sauce nor the cakes look fresh

...except for Hamlet verbs, where a plural verb is only used IF ALL SUBJECTS ARE PLURAL:
either Ben or the twins is guilty; either the twins or Ben is guilty; either the twins or the cousins are guilty
neither the pens nor the pencil is red; neither the pen nor the pencils is red; neither the pens nor the pencils are red

COLLECTIVE NOUNS ARE SINGULAR IF ACTING AS ONE UNIT, PLURAL IF ACTING AS INDIVIDUALS:
ACTING AS ONE: the audience cheers; the team loves Coach Bryant; the mob seems angry; the pack is asleep 
ACTING AS INDIVIDUALS: the audience stagger out; the team hug Coach Bryant; the mob sense danger; the pack are sharp-eyed

ACADEMIC OR SOCIAL DISCIPLINES ARE ALWAYS SINGULAR EVEN IF THEY APPEAR TO BE PLURAL:
physics frustrates me; logistics requires resilience; politics looks exhausting; civics is my favorite class 

NUMERICAL MEASUREMENTS AS SUBJECTS ARE ALWAYS SINGULAR EVEN IF THEIR UNIT IS PLURAL:
thirteen gallons costs $25; five hundred dollars satisfies the debt; ten miles looks far; five years is nothing
EXCEPTION: Percentages and fractions are plural if the unit is plural, singular if the unit is singular 
EXCEPTION: A number of... is plural (a number of student are upset) but the number of is singular (the number of students is seven) 

How to Pluralize Verbs in American English

A regular verb is pluralized by adding an -s to the end:
jump → jumps; befriend → befriends; laugh → laughs

If the verb already ends in an s or ends in a ch, sh, x, or z, the word is pluralized with an -es at the end:
kiss → kisses; reach → reaches; crush → crushes; flex → flexes; buzz → buzzes

If the noun ends in y, look at the previous letter:

• If the previous letter is a vowel, just add an -s to the end: say → says; employ → employs; prey → preys
• If the previous letter is a consonant, then drop the y and add an -ies to the end: carry → carries; dry → dries

If the noun ends in o, look at the previous letter:

• If the previous letter is a vowel, just add an -s to the end: moo → moos; boo → boos; cameo → cameos
• If the previous letter is a consonant, then add an -es to the end: echo → echoes; veto → vetoes; go → goes

If the noun ends in -f or -fe, always add -s: fluff → fluffs; knife → knifes; woof → woofs; wolfs → wolfs​

For phrasal verbs made of nouns plus another part of speech, pluralize the verb part: break up → breaks up; blot out → blots out; pass away → passes away

The only verbs that cannot be pluralized in these ways are "to be" verbs (Hamlet verbs). That's because the eight Hamlet verbs came from three different languages, all of which had different conjugation rules. Here are their rules: I always pairs with am or was (unless joined to another subject by and); for everything else, PAST TENSE: was is singular, were is plural; PRESENT: is is singular, are is plural, be can be either; FUTURE: always MODAL VERB + be. 

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TENSE: shows time

Verb tense shows when the verb occurred relative to now. There are three general tenses: present, past, and future.

Present tense shows a current action that is happening right now.  

• The pure present form of a verb is just its base form: boys run, girls skip, dogs swim.
• Plural present verbs add an -s to the end of the pure present form—this is covered in the above section
• To show that an action is continuous and ongoing, the inflection -ing is added to the verb to form a present participle, as in running, skipping, or swimming (see the section on aspect).
• Note that participles are only kind of verbs—they are technically verbals, which are discussed here.

Past tense shows a previous action that already happened.

• To show past tense in English, we add the inflection -ed (or just -d if the verb ends in e). These are pure past verbs: walked, massaged, emailed.
• Some English words with Anglo-Saxon, French, or foreign origins kept their original past inflections: the words, like eat/ate, run/ran, break/broke, ride/rode, and bit, are called irregular or strong verbs. 
• Some past verbs are combined with a form of have to form a past participle, which shows a fully completed action, as in has eaten or have broken (see the next section on aspect).

Future tense show an action that is yet to be.

• While other languages indicate this with a certain inflection or suffix, English shows this through the addition of a helping verbs. Will and shall are the most common future tense indicators and show absolute certainty that the action is going to happen (Dan will run, Katie shall skip). Other helping verbs can also show future tense in certain contexts (Dan might run for office) but do not show future actions in other contexts (Dan could run for office).

How to Add -ed and -ing to Verbs

Most verbs can be turned into particples by adding an -ed (past) or an -ing (present) to the end:
jump → jumped → jumping; befriend → befriended→ befriending; laugh → laughed → laughing

If the verb ends in -e, look at the letter before: 

• ENDS IN UE OR PREVIOUS LETTER IS CONSONANT:  drop the end E before adding -ed/-ing:​ create → created → creating; rescue → rescued → rescuing
• ENDS IN EE or OE: just add -d/-ing to the end: canoe → canoed → canoeing; agree → agreed → agreeing;
• ENDS IN IE, -ING ONLY: change the I to a Y, then add -ing to the end: die → dying;  vie → vying
• ENDS IN YE, -ING ONLY: do not drop the e before adding -ing to the end: dye → dyeing;  eye → eyeing
  

If the verb ends in -c, add -ked/-king: mimic → mimicked → mimicking; panic → panicked → panicking

If the verb is a single syllable or stressed on the last syllable, look at the last three letters:

• CONSONANT-VOWEL-CONSONANT: double the last consonant before adding the -ed/-ing suffix: star → starred → starring; spot → spotted → spotting; regret → regretted → regretting 

• ...UNLESS THE LAST LETTER IS W, X, OR Y: paw → pawed → pawing; fix → fixed → fixing; delay → delayed → delaying 
• ANY OTHER COMBINATION/NO STRESS: use the normal process: open → opened → opening

Any verb that doesn't follow these rules is a strong verb.

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ASPECT: shows duration

If tense shows when an action occurred, verb aspect shows how the verb moves through time (duration). Unlike many languages, where verb aspect is determined by an inflection or suffix, aspect in English is accomplished by the addition of helping verbs. Here are the five aspects that occur in English:

• Simple (perfective) aspect describes a single action (I finished my drawing). Most verbs are simple aspect, as this describes verbs that have no associated helping verbs (other than will or shall).
• Progressive aspect describes an action that is continuously unfolding (I am finishing my drawing). To show progressive aspect, one of the six BE verbs (am, are, was, were, is, be) must be added to a present participle
• Perfect aspect describes a prior completed action (I have finished my drawing). To show perfect aspect, had or have must be added to a past tense verb to form a past participle
• Perfect progressive aspect describes an action that was unfolding but is now completed (I had been finishing my drawing). To show perfect progressive aspect, had been or have been must be added to a present participle
• Habitual aspect describes an action that regularly happens off and on. English only retains two expressions of habitual aspect, used to and going to (I used to love drawing, I'm going to work at Samson's)

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VALENCY: shows arguments

Valency shows the number of arguments a verb takes, i.e., how many "things" in the sentence an action affects, with things defined as subjects and objects found in the clause.

• TRIVALENT (3 ARGUMENTS): The most arguments a verb can accept in English is three, and these verbs are known as ditransitive. Ditransitive verbs are actions that originate from a subject and affect both direct objects (which receive the action) and indirect objects (which have the object sent to them via the action). For example, threw is a ditransitive verb in I threw Mike the frisbee: I delivered the action, the frisbee received the action, and the frisbee was thrown at Mike so he could receive it. A less obvious ditransitive verb is gave in Stephanie gave me an order: Stephanie was the one who gave, the order was the object given (even if it's an abstract object), and I (or, rather, me) was given the order. Note that stative verbs like gave can be diatransitive along with dynamic verbs).
• DIVALENT (2 ARGUMENTS): A transitive verb is an action performed by a subject and acts upon either one or more direct objects. For example, I tossed the glitter has I as the one tossing, and the glitter as the thing getting tossed, but unlike the ditransitive verb, no one is receiving the glitter. Since the action in singular, it doesn't matter how many direct objects (or subjects, for that matter) there are—they all count as a single argument, just as every piece of glitter in the last sentence counted as one object. For example, Billy sprayed Becca, Beth, and Bobbi with water has all three receiving the same action (getting sprayed) from the same subject (Billy). Like ditransitive verbs, both dynamic verbs and stative verbs can be transitive (e.g., Tommy loves bluegrass music).
• MONOVALENT (1 ARGUMENT): An intransitive verb is an action done by a subject that doesn't affect anything else. (e.g., I smell great, Pete was right, Stephanie runs). ALL LINKING VERBS ARE INTRANSITIVE, as by definition, they can only describe states of existence, not intentional actions. Dynamic and stative verbs can also be intransitive verbs.

So that's it for valency—three tiers. Surely every verb has at least one argument since it must be grammatically paired with a subject...right?

Nope.

• AVALENT (0 ARGUMENTS): English is one of the few languages that adheres firmly to "every action needs an actor" rule. Other languages have lots of verbs that are avalent, or just happen without a specific actor—thus, there are no arguments. Sometimes, these are called weather verbs because weather conditions are the most common type of avalent verb in every language: it snows, it rained, it is thundering. However, there are other ways we use avalent verbs: it dawned on her, it appears that you must choose, there remains just one option, it just so happens that I know her, there exist many possibilities. As these verbs could break English's most essential grammatical convention—that every verb needs a subject—the word it or there is thrown in as a meaningless placeholder. This is called a dummy subject, and these verbs that take no arguments are called impersonal verbs.

So why does valency matter? It doesn't most of the time, as a majority of verbs in English are ambitransitive, meaning they could be used both transitively (Sarah played her flute, Katy writes short stories) and intransitively (Sarah played, Katy writes). However, some verbs are only transitive or intransitive, and using the wrong one leads to common errors in English:

• LAY/LIE: Lay is transitive and requires an object (Chickens lay eggs). Lie is intransitive and is not about setting down an object but a person or creature choosing to recline on their own (Let sleeping dogs lie). This distinction holds true even when, say, a person is placed by others in a reclined position (Have the paramedics lay Mr. Johnson on the stretcher). This is the most common valency mistake in English, partly because lay is the past tense of the base verb lie (the past tense of lay is laid).
• SET/SIT: Just like with lay/lie, set is transitive and applies to/requires objects (Bill, set the book on the couch); sit is intransitive and is an action one undertakes themselves (Bill, sit down on the couch)
• RAISE/RISE: Raise is transitive and applies to/requires objects (Let's raise the roof!); rise is intransitive and is an action by the subject on itself (Let's rise up and fight!)

Valence is also important when looking at passive and active voice (see the next section).

either transitive or intransitive, and a clause is an incomplete fragment if it has a transitive verb without an object. There is an exception: an ergative verb can act upon a single noun transitively if an object or intransitively if a subject (The doorbell rang vs They rang the doorbell).

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MOOD: shows meaning

Verb mood indicates tonal meaning. As verbs are needed for every sentence, sentence meaning is intrinsically linked to the verb. While verb mood is not the same as sentence purpose, there is some crossover between the two ideas.

• ​Indicative mood indicates facts or the state of reality (A car passes by my house; Mike kissed his wife goodbye)
• Imperative mood indicates a command (Don’t push that button; We must stop the mad bomber).
• Conditional mood indicates a state that causes something else to happen (The package might explode early if the button is pushed; Should the captain discover our treachery, we will all suffer).
• Subjunctive mood indicates a hypothetical reality—a wish or dream (I wish that Mr. Coon gave us less homework; If I were a teacher, I would never give homework).

What about VOICE, as in passive voice and active voice?

Grammarians do not define voice as one of their definitions of a verb, as voice is contextually important to a sentence but is not grammatically important. Essentially, there are two voices: active voice occurs when the subject of a sentence does the action, while passive voice occurs when the subject of the sentence receives the action. 

PASSIVE: Megan was devoured by the giant moth creature.
ACTIVE: The giant moth creature devoured Megan. (BETTER CHOICE)

PASSIVE: The poem "If" was written by Rudyard Kipling in 1895. 
ACTIVE: Rudyard Kipling wrote his poem "If" in 1895. (BETTER CHOICE)

PASSIVE: My homework will be done by me.
ACTIVE: I will do my homework. (BETTER CHOICE)

Most writing teachers and editors prefer active voice, as it makes sentences shorter and directs attention to the subject better. However, passive voice has its use: writers intentionally use passive voice to keep the performer of the action hidden (a favorite of mystery writers), when the action should be the focus more than the subject, or to avoid using a vague pronoun without an antecedent. The voice rule of thumb is always do what makes the sentence shorter and clearer.

ACTIVE: The mystery killer stabbed Mr. Body in the throat.
PASSIVE: Mr. Body was stabbed in the throat. (BETTER CHOICE)

ACTIVE: They brew over 1,000 different brands of beer in the Denver area.
PASSIVE:  Over 1,000 different brands of beer are brewed in the Denver area. (BETTER CHOICE)

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FOOTNOTES
1. Why do I call these Hamlet verbs? Hamlet's most famous line is "To be or not to be: that is the question," so it seems fitting to call the "to be" verbs Hamlet verbs. Plus, like Hamlet, they are super old, irregular, and usually passive.
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