Permission, Advice, & Obligation

Meaning

The Deontic Flavor

The Deontic flavor of modal verbs expresses, to various degrees, whether the agent of the sentence (the person carrying out the action) should do the verb. A flavor is a category of modal verbs wherein the uses of the various modals share commonalities in both their meaning and their structure. The term deontic comes from the Greek word for ‘duty’.

Deontic expressions reveal some sort of standard depending on the source, or motivation, of the modal verb:

Internally-Driven Standards: assertions of the speaker’s opinion, personal preferences, moral imperatives, notions of common sense, etc.
Externally-Driven Subjective Standards: rules imposed by some authority, ethical responsibilities, social norms, or widely-regarded best practices, etc.
Externally-Driven Objective Standards: necessary steps in a process, requirements to meet a condition, prerequisites for an end result, etc.

When delivered with a high level of force, these modals can communicate directives and thus are akin to imperatives (like “Eat your vegetables,” or “Stop doing that!”). In their base form, Deontic modals by default indicate a future meaning, whether that is the immediate future, the distant future, or anything between.

Deontic Force

The various expressions of modality each align with a different modal force which conveys the level of the speaker’s conviction and determines the overall meaning. Keep in mind that the exact level of strength isn’t fixed, but can fluctuate depending the the speaker’s intonation. Modal expressions of the same force are broadly considered synonyms, but there are distinctions among them.

POTENTIAL FORCE and WEAK FORCE*: the verb phrase is permitted.
- can/could — externally-based permission
- may/might — internally-based permission
- get to — benevolent permission
MODERATE FORCE: the verb phrase is recommended.
- should — subjective advice
- ought [to] — objective advice
- had better — advice to avoid negative consequences
COMPELLING FORCE: the verb phrase is required.
- must — formal necessity
- need to — objective requirement
- have to — informal necessity
- have got to — impulsive compulsion
CONTROLLING FORCE: the verb phrase is expected to be followed without question.
- will/would — general commands
- shall — legal mandates
- be to — formal demands

In the Deontic flavor, internally-motivated modals tend to care more weight than externally-motivate ones. For instance, may and should are more compelling than can and ought [to], respectively.

Notice that some words come in pairs. Can, may, and will are ‘proximal’ modals and convey a high level of conviction. Therefore, in most situations they are a better fit for Deontic expressions than their counterparts. Could, might, and would are ‘distal’ modals and are more deferential, and are therefore more likely to appear in questions. For past regulations, we use distal modals, not proximal modals, in their Perfect Modal form.

* For other modal flavors, the potential force and the weak force are distinct. However, for Deontic Modals, they are virtually indistinguishable.

Deontic Negatives

There are two different ways that negators (like not and never) can affect verb phrases with modals:

Event Negation — the main verb is negated; modality expresses an obligation not to do something (prohibition), advice to not do something, and similar restrictions.
Modal Negation — the modal verb is negated, which often makes the entire clause inert; modality expresses a lack of necessity, which means the agent is free to do or not do the verb at their own discretion.

Most modal expressions, including all nine core modals, enact event negation. Only need, have to, have got to, and need to enact modal negation. Therefore, if a rule-follower is told, “You must not eat this apple,” they will not eat the apple; but if they are told, “You don’t have to eat this apple,” they may or may not eat that apple depending on their personal preference.

Deontic negation works a little differently for past situations. There’s not a clear pattern here, but for the half of the modals that can even be used in the past:

the agent “shouldn’t have”, “wouldn’t have”, “need not have”, or “oughtn’t have” … but they did;
the agent “didn’t get to” … so they didn’t;
the agent “was not to”, “didn’t have to”, or “didn’t need to” … and they may or may not have done it;
the agent “had better not have” … and the speaker doesn’t know whether the agent did or didn’t.

Structure

Modal verbs come at the start of their verb strings. The core modals are true auxiliary verbs. Pseudo-modals take the position of auxiliary verbs, even though the don’t really function the same way auxiliaries do. Marginal modals lie in between.

Core Modals

can/could
may/might
must
shall
should
will/would

Marginal Modals

had better
need
ought [to]

Pseudo-Modals

be
get
have
have got
need

Notice that there are two versions of need. The archaic version behaves mostly like a modal auxiliary verb while the modern version behaves like a common lexical verb. See the ‘Advance Concepts’ section for details in the differences. These days, most English speakers never use the archaic version.

Also note that the pseudo-modal be, which is always followed by a Full Infinitive, is different from the auxiliary verb BE.

Verb Forms

Details about the form depend on whether a core modal, marginal modal, or pseudo-modal is used.

Defectiveness:
1. Core and marginal modals are defective, which means they only come in their base forms (and subject-verb agreement doesn’t change that).
2. Pseudo-modals take on different forms just like normal verbs do, including taking the -s form following 3^rd-person singular subjects.
Negation:
1. For core modals, marginal modals, and be, the negator comes after the modal (as in “may not” and “shouldn’t”).
2. For pseudo-modals (except be), we use DO + a negator before the pseudo-modal (as in “don’t get to” and “doesn’t have to”).
the Following Verb:
1. After the core modals, had better, and need, the next verb should be in its Bare Infinitive form.
2. After ought [to] and all pseudo-modals, the next verb should be in its Full Infinitive form.

Keep in mind that the verb immediately following a modal is often the main verb, but not always; instead, it might be another auxiliary verb. In that case, that next auxiliary takes on the necessary infinitive form while the main verb could be in any verb form to communicate any tense or voice. For instance, we might have “will have taken”, “can be taken”, “may be taking”, etc.

Past Modals

When expressing past regulations, there are two different forms we might use:

Pseudo-modals undergo the same changes as any other lexical verb (taking the -ed ending, if regular) to express the past, as in “She was to report to the commander’s office by daybreak,” or “We got to go backstage!” or “Thanks, I needed to hear that.”
Distal core modals (could, might, should, and would) and the marginal modals are followed by ‘have’ to form Perfect Modals. The following verb should then be in the Perfect Participle form.
- The Perfect ‘have’ is always in its base form; never ‘has’ or ‘had’.
- ‘Have’ can come in its contracted form, as in “should’ve” or “had better’ve”.
- For ought [to], the word ‘have’ comes after ‘to’, as in “He ought to have known better.”

Proximal core modals (can, may, must, shall, and will) are not used for Deontic past. Neither is the pseudo-modal have got to, which is only used for the immediate future

A couple caveats: a) As a negative, the Deontic “couldn’t” can indicate the past even without being a Perfect Modal; it’s the only core modal that acts this way. b) In extremely casual speech, we can drop the ‘had’ of had better when it’s past, as in “better have” or “better not have”.

Periphrastic Substitutes

Since modal verbs are defective — meaning they do not change form for tense or for subject-verb agreement — they can be awkward or otherwise difficult to use in some situations. Other limitations arise since the proximal core modals don’t work for the Deontic past.

For these reasons and more, core and marginal modals can be substituted with periphrastic expressions, or multi-word phrases that communicate the same basic meaning as modal verbs. Suitable options for the Deontic flavor include (but are not limited to):

be allowed to / be permitted to
be advised to
be supposed to / be expected to
be required to
be going to
negative: be forbidden to

Pseudo-modals (get to, have to, have got to, and need to) can also be used as substitutes for core and marginal modals. See the Modal Adjectives section below for more ways to express modality.

Usage

Permission & Restriction

The modals can, could, may, and might communicate permission. They are often used in questions by those requesting permission, and then in declarative responses by those with the power to grant permission. When made negative, they instead convey a restriction for the following main verb. These four modals have similar meanings to each other in the Deontic flavor, but there are slight differences:

May and might tend to appeal to the would-be permission-granter on a personal level. “May I call you some time?” has virtually the same meaning as “Would you mind if I called you sometime?”
Can and could are more suitable when depending on circumstances that might be beyond the granter’s control. A security guard who says “You can’t go in there yet,” doesn’t express their personal preference, but instead defers to their superiors or the rules of their environment.

Furthermore, the distal modals could and might express more deference than their corresponding can and may. “Could I borrow this for a minute?” is considered more cautious or polite than “Can I borrow this for a minute?” Using might for permission is very formal and is rare in modern English.

The pseudo-modal get can also be used for permission, but rarely for requesting or granting it. Instead, something like “I get to take a vacation next week!” is a statement of permission already granted.

Advice

The modal should (or shouldn’t) is commonly used for giving advice or recommendations, as in “You should try something new,” or “You shouldn’t eat so much chocolate.” The marginal modal ought [to] can also be used this way, as in “You ought to try something new.”

Guidance for actions that have clear and impending negative consequences if the advice is ignored might be expressed with had better (or, in some dialects: had best).

Advice is not enforced, and the agent is not necessarily expected to follow that recommendation. Should, ought [to], and had better communicate an ideal and might guide the agent, but they are not necessarily under any obligation to follow out the advised action.

Obligation & Prohibition

Many of the modals, along with the Deontic marginal modals and pseudo-modals, can convey obligations.

Moderate obligations are expressed with should, ought to, or need [archaic]. (These are similar to advice, except that they are externally motivated rather than an expression of personal opinion.)
- Obligations with clear and impending negative consequences if not followed might be expressed with had better.
Strong obligations are expressed with must, have, have got, and need. See the Advanced Concepts section below on the differences between these.

Some examples of obligations include “We must inform maintenance of the problem,” “You ought to have a good explanation for this!” and “I have to tell her how I feel about her.” Obligations like these may or may not be enforced, but what matters is that the speaker feels compelled to see the matter through, or at least to relay the information.

When negated, some of these terms convey prohibition or forbiddance, while others convey a lack of obligation (and thus place the agent in a neutral position):

Prohibition

Shouldn’t, ought not (to), mustn’t, and had better not express prohibition. They share a similar meaning with the restrictive can’t or may not.

In the example “You mustn’t press that button,” the agent is prohibited from pressing the button, and they cannot press it without breaking the rules.

No Obligation

Needn’t [archaic], don’t have, and don’t need express a lack of obligation or prohibition.

In the example “You don’t need to fill out that form,” the agent is freed from any obligation one way or the other; with any regulation lifted, they may choose to fill out the form or not.

Obligations and prohibitions expressed in a past form are Modals of Reproach.

Reproach

When Deontic Modals are expressed as past, they convey some sort of disapproval over a past action (or an action that was not taken). When the agent is ‘I’, or sometimes ‘we’, these generally express regret. Deontic Modals should be in their Perfect Modal form for this, i.e. they are followed by ‘have’ (but pseudo-modals can undergo the usual verb transformations into their past forms). For example:

“He could’ve taken a quicker path,” conveys a missed opportunity.
“I ought to have been more careful,” conveys regret.
“You shouldn’t have been so harsh with your sister,” conveys criticism.
“You didn’t have to shout,” conveys rebuke.
“She needed to prime the pump first,” explains what went wrong.

Should’ve is the most common modal used for reproach.

In the Deontic flavor, core and marginal Perfect Modals typically indicate an unreal past, referring to something that didn’t actually happen (but perhaps should have). Meanwhile, the pseudo-modals are more likely to be real. For example, “Zhan should’ve joined us,” indicates that Zhan didn’t join them; but “Zhan had to join us,” could be used whether she joined the speaker or not.

We can instead you had better have, or simply better have, to express ideals for past actions when the speaker is unaware of whether the action was carried out or not. For instance, if Marcelle says, “You better have saved the document before the power outage!”, she doesn’t yet know whether the document was in fact saved, and so her concern is not yet resolved into either disapproval or relief.

	Affirmative Past		Negative Past
could	could’ve	but didn’t	couldn’t	but did
should	should’ve	but didn’t	shouldn’t have	but did
would	would’ve	but didn’t	wouldn’t have	but did
had better	(‘d) better have	(uncertain)	(‘d) better not have	(uncertain)
need	–	–	needn’t have	but did
ought [to]	ought to have	but didn’t	ought not have	but did
be to	was/were to	(either)	was/were not to	(either)
get to	got to	and did	didn’t get to	and didn’t
have to	had to	(either)	didn’t have to	(either)
need to	needed to	(either)	didn’t need to	(either)

When negative, past core modals and need and ought [to] usually refer to actions that did happen, but probably shouldn’t have. But negative past pseudo-modals could be used whether the action happened or not … except that didn’t get to suggests that the action didn’t happen.

Process Requirements

Sometimes requirements have nothing to do with rules or even preferences; they might just be the necessary steps to get a thing done. This is sometimes called the Teleological flavor, but we at Insights consider it to be a subset of the Deontic flavor.

Teleological modals reflect the nature of the thing being done, like the necessary steps of a process or the condition required to reach a certain result. They often accompany cause-and-effect constructions and thus are common to embedded clauses or might accompany expressions of Purpose or Result. For example:

“I still need to pick up some supplies for tomorrow’s party.”
“If you want to make a strong impression, you ought to wear something sharp.”

Commission

The modals shall and will impart commands, especially when the subject of the clause is ‘you’. For example, “You will stop that this instant!” or “You shall wait here until your name is called.” Shall is extremely formal, but even will is not often used in this way; instead, English speakers usually use the imperative structure to issue commands, as in “Stop that this instant!” or “Wait here until your name is called.”

When 1^st-person pronouns are used, shall, will, and would can express a resolve to do something, like “We shall never speak of this again,” or “I would listen to their plea.” Again, these feel outdated, and modern English speakers do not often use modals like this.

Similar to commissions like these are Volitional Modals of intent, like “I will exercise more this year.” While this will probably arises from some inward motivation, the Deontic will (or would or shall) arises from some sense of obligation.

Alternatives

Advanced Concepts

Have To vs. Need To vs. Must

The terms have to, have got to, and need to are loosely synonymous with must when used as positives. One benefit to those pseudo-modals is that they are not defective (they can take on different forms), and thus can be used for double modality. For instance, we can say, “She might have to leave,” or “She might need to leave,” but not “~~She might must leave.~~“

It’s a different story for negatives, though. Remember that mustn’t conveys negative obligation, or prohibition, while don’t have to and don’t need to convey a lack of obligation one way or the other and thus are neutral.

But even as positives, there are some key differences between these terms:

MUST is generic enough that it applies to a wide range of applications for necessity. It’s not necessarily formal, but it’s certainly not as casual as have to, have got to, or need to, and thus it carries more gravitas when external regulations matter. Examples include: “We must be careful not to wake the dog,” and “Museum patrons must refrain from touching the exhibits.”
HAVE TO is interchangeable with must in nearly every situation, but there is a slight difference in that have to is often biased. It may be used to convey the speaker’s own desires. Or, when relaying external regulations, the right intonation might indicate what the speaker feels about established rules or the expectations of an authority figure (such as excitement or disapproval). Examples include: “Janelle has to come visit as soon as possible,” and “Sorry, but you’ll have to try again tomorrow.”
HAVE GOT TO is different from the others because it is usually impulsive. The reason behind the necessity may have only just arisen, or perhaps there is some urgency to the proposed task. Have got to is very subjective and often accompanies heightened emotions. Examples include: “The movie sounds amazing; I’ve got to see it!” and “You‘ve got to get out of the restricted zone before you’re discovered!”
NEED TO is best used for requirements that lead to desired or recommended results, and thus are very objective. Need to might introduce a necessary step of a process or establish the condition of a cause-and-effect relationship. Examples include: “You need to show your ID to get into the club,” and “Graham needs to buy some groceries for tonight’s dinner.”

Despite their differences, the line between these terms can be fuzzy in some applications; there are plenty of instances where one of these can be substituted for another without drastically changing the meaning. Often, the way in which the speaker voices the obligation (including their tone, intonation, and emphasis) communicates their intent just as well as, if not more than, their word choice.

Need: Archaic vs. Modern

Notice that there are two versions of need, and they have identical meanings. The archaic version mostly behaves like an auxiliary verb (meaning that it can have not after it or even contracted to it, and it can undergo subject-auxiliary inversion) and like a modal verb in that it does not inflect and is followed by a Bare Infinitive. The other version behaves like a normal lexical verb in a Verb Pattern.

archaic Marginal Modal ‘Need‘	Pseudo-Modal ‘Need (to)‘
followed by the Bare Infinitive, as in “need explain“	followed by the Full Infinitive, as in “need to explain“
for negative: not (or never) follows the modal, as in “needn’t explain”	for negative: DO not (or never) comes before need, as in “don’t need to explain”
can invert with the subject for situations like some questions forms, as in “Need I explain?”	cannot invert with the subject for situations like some questions forms: “Do I need to explain?”
does not inflect based on person of subject, as in “They need explain” vs. “She need explain”	does inflect based on person of subject, as in “They need to explain” vs. “She needs to explain”
made past as a Perfect Modal, as in “need have explained”	made past like normal verbs, as in “needed to explain”

The archaic version is rarely used in modern English. Even when it is used, it’s typically for questions and negatives only. It’s possible that language learners might encounter the archaic need on occasion, perhaps through classic literature. But for the most part, the archaic need doesn’t need to be taught in English classes.

Passive Regulations

Of all the modal flavors, the Deontic Flavor is the most likely to incorporate Passive Voice. So instead of saying, “Someone needs to feed the cat while we’re gone,” we might say, “The cat needs to be fed while we’re gone.” The big difference is that the target of the action is now at the front of the sentence as the new subject. The modal stays the same (though the form of a pseudo-modal might need to change to agree with its new subject), as does the way it’s negated, if appliable. But the modal should then be followed by the Passive BE, and the main verb should be in its Passive Participle form. For more, visit our Passive Voice page.

Similarly, we might use the Causative Structure together with Deontic modality, as in “We should get our car fixed this weekend.”

Elsewhere on this page, you may see references to ‘the agent’, which is simply the noun that carries out the verb. In most cases, the agent is the subject of the clause. But with Passive Voice, the subject is not the agent; the agent might be expressed after the preposition ‘by’, but most of the time it is unvoiced (perhaps because it is not known yet, or perhaps because it is obvious).

Passive Voice cannot be used with get to, which needs its agent to also be its subject.

Intrinsic Necessity

A sister category to Deontic necessity is Intrinsic Necessity, a part of the Alethic flavor. This flavor communicates requirements in a very similar way. But the key difference is that those requirements reflect the intrinsic nature of the situation, rather than the regulations of authority, society, ethics, personal preference, etc.

Modality expresses the speaker’s conviction regarding the verb phrase. The Alethic flavor is tangential to pure modality because it does not reflect the speaker’s beliefs, standards, or perception. In fact, the speaker has nothing to do with it. Nevertheless, we often use modal verbs to convey Intrinsic Necessity.

For example:

“We can enter the shop any time during the hours of operation.”
“You have to turn the key to start the car.”
“Cake batter must include flour.”

Teaching Tips

Separate Flavors, Consistent Force

Students may recognize that modals are used in different ways. They are probably first introduced to can as a Modal of Ability, but now they can see its also a Modal of Permission. Perhaps they also know it can be a Modal of Possibility. This might seem confusing, so you may want to make it clear that these are three different uses of can.

Point out that there are other words with multiple meanings like ‘right’ (opposite of ‘left’ or opposite of ‘wrong’), ‘light’ (opposite of ‘dark’ or opposite of ‘heavy’), ‘trunk’ (of an elephant or of a tree) and plenty of others. Each of the core modals is like that.

Also, it may help to communicate that each modal verb has consistent force across all its meanings. For example, must is always strong, so it probably wouldn’t be used if the speaker feels ambivalent. Conversely, may and might are weak, so someone with absolute conviction wouldn’t use either of them to argue their point, no matter which flavor is relevant in that situation.

Bit by Bit

As complex as the application of modal verbs are, it’s probably best to teach them a little bit at a time, going just a bit deeper with each proficiency level that students advance through. For instance, you might want to start with basic applications of core modals the positive form, then later introduce the negations, then later introduce common periphrastic substitutes, then later still cover Perfect Modals and past applications.

Thankfully, most coursebook series use this method across multiple levels of their books.

Sliding Scales

Consider the different strengths of modal force for the Deontic flavor, and have your students place them in order or otherwise identify the distinctions between them.

Visual Order

Have the students write the modals in order from top to bottom (modal pairs can stick together). Alternatively, you can write each modal (or pair) on a card and have the students arrange the cards from top to bottom. At the top, the agent will definitely do the thing because they don’t have much of a choice, but at the bottom the choice is their own.
At a higher proficiency level, add in the negatives. Now, the agent definitely does the verb at the top, definitely does not do the verb at the bottom, and can choose whether to do verbs in the middle.
Also at higher levels, add in marginal modals and pseudo-modals.

Act It Out

Have two students at the front of the classroom, one who definitely wants to do a specified verb, and one who definitely doesn’t want to do that same verb. A third student uses a Deontic modal with that verb, and then the students act out doing the verb or not, depending on the regulation.
For example if the modal is must, both students should do the thing; but if the modal is may, only the student who wants to do the thing should do it.

English Grammar Encyclopedia for Educators