Explication of modalities

This original article is about explication of modalities with the help of nouns, adjectives and verbs and by other means. Modalities to be explicated include must, shall, should, should better, ought to, can, may, could, might and also have to. They stand in contrast to imperatives; arguably, an imperative has a semantics very different from those of the modalities. At the same time, the semantics of imperatives and certain modalities seem to have something in common.

An example of an explication is this: "X must do Y" can be explicated as "It is X's duty to do Y". Thus, must has been explicated as duty. A further step would be an explication of duty. One possible explication is this: If X does not do his duty, Y will punish X. But what is "punish"? Y will punish X by causing displeasure to X; there are possibly other forms of punishment.

Candidate semantics of the modalities can be found in dictionaries. In this article, there is the opportunity to treat all modalities as a whole, a group, and deepen the analysis as required or expedient, beyond dictionary format.

Explication via nouns, adjectives and verbs

The following nouns are candidates for explication of the modalities:

• necessity (must)
  • epistemic necessity
  • ontological necessity
  • deontic necessity
• possibility (can)
• contingency
• duty (must, ought to)
• obligation (must, ought to)
• option (can)
• ability (can)
• expediency (should?)
• requirement (shall)
• rule
• recommendation (should)
• hint (may?)
• prohibition (must not)
• allowance (may)
• permission (may)
• prediction
• likelihood, probability
• certainty
• advisability
• prudence
• desirability

The following adjectives are candidates for explication of the modalities:

• necessary
• possible
• contingent
• obligatory
• mandatory
• optional
• allowed
• disallowed, prohibited
• recommended
• strongly recommended
• discouraged
• ideal
• useful
• optimal
• required
• expedient
• right
• likely, probable
• certain
• advisable
• prudent
• desirable

Even some verbs are candidates:

• behove

The above tentative and sketchy explication suggests ways of making text less ambiguous, by replacing modal verbs (auxiliaries) with nouns or adjectives, both of which tend to be less ambiguous. In certain contexts such as formal specifications, modalities are normatively assigned narrower meanings, more restricted than the possible meanings given by dictionaries.

Semantics of imperatives

Imperatives seem to have some semantic similarity to modalities, so seem worth having a closer look at. The default semantics of imperatives seem to be one of a command, whether as part of a family (from parents to children) or as part of a chain of command, e.g. in military settings or corporate settings. The implication is that the entity issuing the command has the authority to do so and the entity receiving the command accepts that authority without performing a deeper independent verification of the general validity of the command. This kind of subordination may be important in military settings, where a command by a lead soldier may need to be rapidly transferred into action by a subordinate soldier.

The above semantics seems to differ sharply from e.g. the semantics of ought and duty. Ought-statements seem to lay claim to general validity, whatever may be meant by that. An ought-statement may be disputed for implied accuracy, validity or acceptability; by contrast, a command derives its authority not so much from itself but rather from the entity issuing the command.

Pragmatics

The pragmatics of imperatives can differ from the semantics. Thus, if a friend states an imperative toward another friend, it is unlikely to be interpreted as a genuine command but rather as a wish or a proposal. The other way around, if a powerful abusive entity issues what on the syntactic face is a mere expression of a wish rather than a command, a subjugated entity may interpret that wish as a command. Thus, if a powerful abusive entity says "I would wish someone would do X for me, wink wink" to a subjugated entity, the subjugated entity may interpret that as a command issued under the pain of penalty, and they may do so without the here implausibly expressly signaled "wink wink". The powerful entity can use a range of indirect phrasings, e.g. "It would be ideal if someone would do X for me".

The difference between semantics and pragmatics also applies to modalities in general, not just imperatives. Thus, if a customer asks a sales clerk, "could you please give me cigarettes so and so", the effect of that polite wish is of a command since the sales clerk does not have the authority to reject such a wish. The sales clerk is subordinated to the employer and the employer has commanded the clerk to fulfill customer wishes as long as they are legal, meet the business rules and are payed for by the required price.

Joint Strike Fighter Air Vehicle rules

In the context of software development (computer programming) based on formal specifications, Joint Strike Fighter Air Vehicle C++ Coding Standard assigns particular semantics to certain modalities:

• "Should rules are advisory rules. They strongly suggest the recommended way of doing things."
• "Will rules are intended to be mandatory requirements. It is expected that they will be followed, but they do not require verification. They are limited to non-safety-critical requirements that cannot be easily verified (e.g., naming conventions)."
• "Shall rules are mandatory requirements. They must be followed and they require verification (either automatic or manual)."

Above, the "will rules" specification is not entirely clear; how does "intended" make a difference between "will rules" and "shall rules"? What is clear is that "Will rules" are weaker than "Shall rules".

See also

A related subject is that of formal modal logics.

Further reading

• Wikipedia:Modal verb
• Auxiliary | grammar, britannica.com
• Modal verbs: "may," "might," "can," "could," and "ought", Britannica Dictionary
• JOINT STRIKE FIGHTER AIR VEHICLE C++ CODING STANDARD, stroustrup.com -- assigns particular semantics to should, will, and shall