Saeed (1997: 125）considers modality to be a semantic category and a cover term for the linguistic devices which allow speakers or writers to express varying degrees of commitment to, or belief in, a proposition.In discourse, MVs are an important means of conveying attitude, judgment, obligation, necessity and permission.According to Palmer (2003: 7-8), MVs can be classified into three types, namely, deontic, epistemic and dynamic MVs.Deontic MVs express obligation, permission and necessity intended by the speakers or writers concerned, epistemic MVs judgment by the speakers concerned, and dynamic MVs the ability and willingness of the agent concerned:
Epistemic modality is concerned solely with the speaker’s attitude to the status of proposition.Deontic and dynamic modality relate directly to the potentiality of the event signaled by the proposition, but of two different types, both of which may be seen as “directive” ― getting things done.Deontic modality is directive in that the event is controlled by circumstances external to the subject of the sentence (more strictly the person or persons identified by the subject).With Dynamic modality the control is internal to the subject.(Italicized by the writer of this dissertation）(Palmer, 2003: 7-8)
In another work, Palmer (2001）holds that there are two modal systems, namely, propositional and event modality, which include four types of modality:
Epistemic modality and evidential modality are concerned with the speaker’s attitude to the truth-value or factual status of the proposition and may thus be described as ‘propositional modality’…Deontic and dynamic modality refer to events that are not actualized, events that have not taken place but are merely potential, and may thus be described as ‘event modality’.(Italicized by the writer of this dissertation）(Palmer, 2001: 24/70)
Halliday (1994: 356-357）holds that modality can be classified into four types: probability, usuality, obligation and inclination.Probability and usuality are of the ‘indicative’ type in the sense of modalization while obligation and inclination are of the ‘imperative’ type in the sense of modulation.Roughly speaking, probability and usuality correspond to epistemic modality, whereas obligation and inclination are equivalent to deontic and dynamic modality respectively.
MVs are not the sole means that can show modality.MAs such as possibly, probably and surely can express modality as well.Greenbaum (1969）and Perkins (1983）show that MAs express modality mainly by means of two types, namely, adjuncts and disjuncts.Adjuncts include such adverbs as aspectual and formulaic ones; disjuncts consist of such adverbs as manner and attitudinal ones.Halliday (1994）and Halliday & Matthiessen (2004）study the use of projection clauses such as I think, she believes and they doubt, and nouns such as possibility, likelihood and necessity, and adjectives such as possible, likely and necessary in carrying modality at the clause level.
Some linguists have paid attention to studying the functions of multi-layered modality through the co-occurrences of different linguistic devices, for instance, MV + adverb.Nuyts (2001: 175）records how English and Dutch allow the scalar marking of ‘probability’ by highly idiomaticized modal-adverb combinations such as may well and kan goed (the latter being the Dutch version of may well）though he does not go further beyond this stage of research.Also, Paradis (2003）mentions that the adverb really could play a vital role in attesting truth, emphasizing attitude and reinforcing degree, e.g.:
(4）I can’t really handle rum, that’s why I didn’t drink any last night.
(5）There will be one big nuclear war which will last really long and finally end the world.
Paradis (2003）believes that MAs such as really in Examples (4）and (5）are frequently used in expressing modality, and that to a certain extent they have been grammaticalized.However, such co-occurrences between MVs and adverbs are not just patterns of grammaticalization.They should also be regarded as a means of modality supplementing, in which MVs express a central modal meaning and adverbs a subsidiary one.In other words, these adverbs co-occurring with MVs and functioning modally should be considered as a means of modality supplementing, and help to achieve modal synergy.
Consider another two examples involving the use of MSAs:
(6）Oh, I can’t do it yet.
(7）Never before have fans been promised such a feast of speed with reigning World Champion Ove Fundin sparking the flame that could set the meeting alight.
In Example (6), the MSA yet supplements the modality denoted by the MV can.If yet were removed, the clause would indicate the addresser’s inability of performing a certain act as required, maybe forever.However, through the co-occurrence between can and yet, the addresser simply shows the temporary inability of acting, implying the ability in the foreseeable future.Therefore, yet as an MSA changes the strength of modality.To be exact, it weakens the impossibility here.In Example (7), the adverb never before and the MV could appear in different parts of the clause complex, with the latter in the embedded clause.Nevertheless, the impact of the MSA can be felt in decoding the clausal modality.It is the MSA never before in the sense of the past that makes a contrast with the MV could in the sense of the present and ability.Obviously, the MSA never before provides a background for decoding the modality of the MV could.
In short, linguists have normally studied modality from a single perspective, without thinking about the co-functions of various factors.The study of modality through analyzing a single modal device only has four drawbacks:
(A）In real situations, with regards to addresser―addressee relationship, addresser’s purpose, generic needs and situational circumstances, a single modal device may not be sufficient for the interpersonal metafunction;
(B）Modality as a means of displaying subjectivity is not expressed by a single modal device only; rather, it can be conveyed by various parts of speech (e.g.noun, adjective, adverb and verb）and ranks and groups (e.g.verb group, adjective group and clauses);
(C）The use of a single modal device may cause ambiguity or confusion to some extent (for instance, can has the modal meanings of ability, permission and possibility）and discourse participants tend not to behave verbally in this way;