Discourse relations: Genre-specific degrees of overtness in argumentative and narrative discourse

2.1.Discourse relations

In line with SDRT [2] a DR is defined as a logical connection between a proposition p1 as part of a discourse D and some other proposition p2 in D; p1 and p2 may be realized through adjacently or non-adjacently positioned DUs. A DR is thus a function that takes the two propositions under consideration as its arguments. To study the linguistic realization of DRs in naturally occurring discourse, the SDRT-based definition has been supplemented [21] by the functional-grammar concept of coherence strands [13] and the syntactic concept of theme zone [15,16]. On the most fine-grained level of analysis, DUs which realize propositions that are linked through a DR are referred to as elementary DUs. These typically take the form of clauses, but may also be realized as subclausal (or: “clause-like” [23]) units, such as complex noun phrases. Elementary DUs may combine to realize DRs on coarser levels, with DRs spanning across several clauses or paragraphs, which in themselves form more complex propositions.

DRs in SDRT are classified according to their semantics, their “defining conditions” in our terms. SDRT’s taxonomy is thus not as fine-grained as that of Rhetorical Structure Theory (RST) [22], which, for example, “distinguishes among several Contrast relations, for instance contrast, antithesis and concession. These relations differ on the basis of quite subtle differences in their underlying semantic dissimilarity, but not with respect to the communicative intentions realized” ([2], p. 145). Table 1 systematizes the most frequent DRs with respect to their defining conditions and illustrates how DRs in SDRT categorize into coordinating and sub-/superordinating, depending on whether DUs keep the discourse on the same level, or are located on different hierarchical levels.

2.2.Linguistic realization

Linguistically, DRs may be realized implicitly or overtly, depending on whether the defining conditions of a DR are encoded in coherence strands, or additionally signalled with discourse connectives (DCs), metacomments and/or pragmatic word order [21]. Coherence strands, in line with Givón [13], hold across clauses and are made manifest through topic continuity, i.e. topic identity or specification, tense and aspectual coherence (including modality), spatial coherence and lexical coherence, in particular lexical relations such as antonymy, synonymy etc.

Among overt signals, pragmatic word order refers to non-congruently configurated theme zones, which are adopted from Systemic Functional Grammar, in particular multiple themes and theme zone [9,15,16]. They realize both anaphoric and cataphoric reference by connecting what has just been said/written with what is going to be said/written. Similarly, DCs function relationally in that they index metacommunicative information about the speaker’s attitude towards a DU or how DUs are to be related. They fulfil discourse-management functions and provide instructions for discourse processing and construal of discourse coherence. They may trigger generalized conversational implicatures for the structuring of discourse, and for attitude specification towards propositions and participants.

As an example, Contrast in (1) is realized overtly. Its defining condition is encoded in topic and referential continuity (‘London’ – ‘it’), temporal discontinuity (‘was’ – ‘is’) and lexical antonymy (‘dowdy’; ‘stale’ – ‘exciting’); a contrastive DC ‘but’ and pragmatic word order (fronted temporal adjuncts ‘in the 1950s’ and ‘today’) additionally signal the defining condition overtly.22 In (2), Explanation is realized implicitly; it is encoded in topic continuity, temporal-aspectual overlap and the lexeme ‘cause’.

As regards their linguistic realization, DRs may be fully specified by indexical reference to all of their defining condition(s); they may even be overspecified if an overt signal is added to their full specification. Since some of the defining conditions of DRs show some overlap (e.g. Continuation and Narration share the defining condition of common topic, but differ in the Narration-defining condition of temporal sequentiality; cf. Table 1), their linguistic realization may also remain underspecified and thus ambiguous unless supplemented by overt signals, which guide the recipients in their assignment of the speaker/writer-intended DR. Depending on the number of conditions and features indexed in discourse, we may thus distinguish between various degrees of specification33 and various degrees of overtness.

2.3.Variation

Research into the linguistic realization of DRs shows that the variation between overt and implicit realizations of DRs is systematic, and appears to be affected by three variables: (1) the semantics of the DR, (2) the adjacent or non-adjacent positioning of the DUs realizing the relation, and (3) the contextual constraints and requirements of genre. Studies on the linguistic realization of DRs in English and German editorials and narratives [32,33], for instance, show that the DR Contrast is always realized overtly, indicating that overt realization is the default for this DR; other DRs such as Explanation are realized overtly in narratives more frequently than in editorials, showing systematic patterns of variation that also correlate with the sequential realization of DRs through adjacently or non-adjacently positioned DUs, with narratives realizing DRs connecting non-adjacently positioned DUs overtly more frequently than editorials. Similar tendencies are observed by [17,21] and [11] in texts elicited in editing-based tasks where participants were asked to “flesh out” bare texts of the respective genres, suggesting that discourse genre constrains the linguistic realization of DRs.

Genre-specific DR realization would mean that there are some discourse genres in which adjacently positioned Elaborations and Continuations are typically signalled overtly, and other discourse genres in which adjacently positioned Elaborations and Continuations are typically encoded, but not additionally signalled; but there is also discourse in which the realizations of the DRs are not in accordance with the typical preferences of the genre. This systematic variation is assumed to manifest itself in varying degrees of overtness of a given type of DR and of all DRs in a genre. The following section will focus on argumentative discourse and correspondences between argumentation structure and discourse structure to prepare the ground for a study of genre-preferential degrees of overtness in the linguistic realization of DRs in the specific context of argumentative discourse.

3.1.Argumentative discourse

Argumentative discourse refers to the discursive realization of argumentation, i.e. discourse with the communicative purpose to negotiate the validity of a standpoint at issue. To achieve this goal, interlocutors may need to provide further evidence to rebut doubts and persuade their communication partner to adopt their standpoint. Structural approaches to argumentation, such as Argument Mining, aim to analyse the structure of argumentative discourse by identifying and segmenting argumentative portions of discourse, and visualizing argumentation structure in diagrams. Annotation schemes, or diagramming techniques, used for these tasks differ depending on underlying frameworks.

While traditional approaches to argumentation structure concentrate mainly on the structural representation of individual arguments put forward in argumentative discourse, which they consider to be made up of a conclusion and one or more premises, dialectical approaches (e.g. [12,26]) strive for a model of how premises and conclusions and the arguments they form combine in larger complexes in an argumentation, i.e. the “macrostructure of argumentation” [12]. They consider argumentation structure as a reflection of the hypothetical exchange between a proponent who presents and supports arguments and an opponent who attacks the proponent’s arguments and their supporting premises. Accordingly, text is segmented in such a way that units of analysis reflect the moves of proponent and of opponent.

Depending on whether argumentative moves defend the proponent’s standpoint or attack it, they classify as Support or Attack. In line with Peldszus and Stede [26], Support moves may directly support a conclusion, realized in a move referred to as Claim, in the form of independent arguments, or they may indirectly support a conclusion by providing a new argument for, or an example in support of, one of its premises. Attack moves directly provide arguments against a conclusion or attack the cogency of a supporting argument, thus indirectly attacking a conclusion. They comprise Rebuttals against the conclusion or a supporting premise, i.e. moves that support the refutation of the conclusion or of one of the premises, and Undercuts, viz. moves that are intended to question the validity of a premise. Counter-attacks, as their name implies, are proponent’s moves that attack the opponent’s attacks.

According to van Eemeren et al. [36], argumentative moves may be signalled by linguistic indicators, viz. “verbal means arguers use to indicate the functions of the various moves that are made in an argumentative discussion or text” ([36], p. 479). These include DCs like but, although and nevertheless, lexical expressions such as cause, effect and leads to, and metacomments like it has not been proven that; they are considered to be operational in the automatic annotation of argumentative moves [8]. The notion of linguistic indicators ties in with other approaches in Argumentation Theory that conceive of argumentative DCs such as but, however, as a consequence as “argumentative connectors” [1], “metalinguistic operators” [25] or “pragmatic connectives” [24] which constrain the argumentative potential of the premises they introduce. Moreover, the idea of metacomments as linguistic indicators is mirrored in “shells” [20], that is high-level organizational elements such as the point is that or the argument states that, which interlocutors may use to explicitly refer to their own or an opponent’s premises and conclusions. As with the overt signalling of DRs, not every move is signalled by a linguistic indicator [36], and a context-independent one-to-one mapping between linguistic indicators and argumentative moves is not feasible.

Linguistic indicators for argumentation and overt DRs signals share similar forms and functions in that both may comprise DCs and metacomments, and in that they overtly signal the connectedness of the units pertaining to their respective level of discourse representation. The following section will explore whether and in what way argumentation structure may correspond with discourse structure.

3.2.Argumentation structure and discourse structure

Argument Mining has investigated possible correspondences between argumentation structure and discourse structure (e.g. [6,14,28,34]). While most studies compare argumentation structure as described in RST [22], Stede et al. [34] examine the relationship between argumentation structure and discourse structure as conceived of in SDRT [2], which will be focal in our study. Annotations of their corpus of argumentative microtexts [27] indicate that edges of units realizing argumentative moves, which may consist of several elementary DUs, coincide with edges of clause-based elementary DUs realizing SDRT-based DRs in 63% of all cases ([34], p. 1056). Depending on their frequency of occurrence in these data, the DRs Contrast, Elaboration, Continuation, Result and Explanation seem most relevant for argumentation, showing systematic variation in their correspondences with argumentative moves (cf. [34], p. 1057). But why should argumentative moves coincide with DRs only in some cases, but not in others, and what may be the cause for varying correspondences?

Peldszus and Stede argue that “distinguishing rhetorical structure [discourse structure in our terms] and argumentation structure is important for capturing the different aspects of a text’s coherence on the one hand, and its pragmatic function on the other” ([28], p. 104). However, while argumentation structure and discourse structure approach argumentative discourse from distinct theoretical perspectives, their units of analysis may coincide. In instances of coinciding units of analysis, i.e. of coinciding stretches of discourse structure and argumentation structure, units are not only assigned discourse-anchored DRs by interlocutors at a local level, but have additional argumentative functions. In (1) analysed above, for instance, the argumentative genre of editorial guides interlocutors to assign the argumentative function of Rebuttal to DUs #1/2 and #1/3 related by Contrast; the DC but thus does not only signal Contrast, but fulfils the function of a linguistic indicator for the Attack move realized in #1/3.

Many defining conditions of DRs are also employed in the definitions of argumentative moves. For instance, the defining condition of topic specification makes Elaboration particularly apt to realize Support moves, with the second DU adding further supportive detail to an argument or a supporting premise expressed in the first. However, Elaboration can also supply additional details that may result in the Rebuttal of an argument or of a supporting premise.

We may conclude that argumentation structure and discourse structure may coincide, and that overt signals may provide important cues for the interpretation of both. Against this background, the accommodation of genre-specific degrees of overtness with regard to the linguistic realization of DRs may be beneficial to annotation.

4.1.Data

Informed by previous studies that suggest differences in the linguistic realization of DRs between argumentative and narrative discourse (e.g. [11]), our contrastive approach compares data from the argumentative genre of editorial with data from the narrative genre of personal narrative.44

Narrative discourse and its realization within the genre of personal narrative are constrained by story-internal configurations, such as number of characters, setting and plot, and by story-external, cultural configurations, such as spoken or written modes or participation format [10]. Following Labov [18], a personal narrative typically contains a reference to a single past event, introduced by a verbal phrase realized in a past tense, and a raison d’être. The past event hinges on a reportable and tellable personal experience, consisting of a series of events in the past that are contingent on one another and recounted from a 1st- or 3rd-person perspective. The sequence of events in the series, generally reflecting the temporal sequence of events, is open to some variation with regard to length and tense shift, but needs to be in accordance with story-internal and -external constraints.

Similar to argumentative discourse, narrative discourse appears to have preferences with respect to overt realization of the connectedness between its constitutive units: chronological sequence between events is typically signalled with clause-initial adverbials of time [7], while DCs such as and, then and next may serve as “segmentation markers” signalling topic continuity and discontinuity [5], indicate shifts in the deictic centre [31] and express involvement on the side of the writer [10]. Editorials and personal narratives are thus expected to exhibit differences with respect to their overt vs. implicit realizations of DRs.

Table 2 summarizes the structure of our dataset. For single-authored data, we draw on English datasets employed by [32,33], comprising a set of 9 editorials from British newspaper The Guardian, and a set of 10 short personal narratives from British university students. Co-constructed data, also collected for previous studies [11,21] contain 9 argumentative and 9 narrative texts jointly produced by 18 participant dyads (9 per genre) of native speakers of English. They were obtained through an editing-based task (cf. Section 4.2) designed to elicit, in a controlled fashion, comparable data that permits evaluation, specification and testing of genre-preferential variation in the linguistic realization DRs derived from the analysis of single-authored data.55

4.2.Editing-based tasks

To elicit argumentative and narrative data comparable to single-authored data, the editing-based tasks employed two ‘bare’ texts adapted from an editorial and a personal narrative written by single authors. These texts were stripped of all extra-clausal constituents such as parentheticals, adverbials of time or place and DCs [21], but retained original sequence and default configuration of events. Strings of bare DUs of this kind presumably reflect a minimum of propositional content and allow for maximal diversity with respect to the interpretation of DR potentials that they refer to indexically.

The editing-based task asked participants to collaboratively add linguistic material to the bare text or alter it in order to create a well-formed text of the specified genre (bare texts and instructions are reproduced in the Appendix). Relying exclusively (1) on sequential ordering of DUs and (2) on semantics of intra-clausal material encoding potential DRs, they had to negotiate possible interpretations of the relations between the DUs to agree on a specific DR, and alter the text where necessary. This allows conclusions about (a) where coherence strands encoded in the bare DUs were perceived to carry defining conditions that were considered sufficient to specify a DR, (b) where they were considered to be less than sufficient and therefore required additional encoding and signalling to specify a DR, and (c) where they were considered to be underspecified for a DR, but still sufficient, thus allowing multiple assignment.

4.3.Annotation

Annotations of both single-authored and co-constructed texts were carried out in line with the theoretical considerations outlined in Section 2. Two annotators independently segmented the text into non-overlapping clause-based elementary DUs and, in line with the taxonomy illustrated in Table 1 (cf. Section 2.1), coded them for coordinating DRs (Continuation, Narration, Contrast and Background) and subordinating DRs (Elaboration, Explanation and Comment).66 Annotations also considered the adjacent vs. non-adjacent positioning of DUs realizing DRs, and DRs’ implicit vs. overt linguistic realizations as reflected in their encoding in coherence strands, and signalling with DCs, metacomments and non-congruently configurated theme zones. Deviating codings were negotiated and aligned at all relevant stages of analysis.

4.4.Analysis

To determine the impact of genre on the implicit vs. overt realizations of DRs, a series of quantitative analyses examine

Because some DRs (Background and Narration) do not occur in all genres and/or modes of production, they may not be considered in all quantitative analyses – especially in statistical analyses that can only take into account DRs that occur in both modes of production/genres – but will be considered in reports on overall degrees of overtness.

5.1.Degrees of overtness in single-authored data

An independent one-way ANOVA comparing degrees of overtness in single-authored editorials and narratives finds a significant impact of genre (F(1,17)=51.82, p<0.0001), with narratives exhibiting higher overall degrees of overtness (79.8%) than editorials (51.6%). This is also supported by a weighted independent measures t-test between genres that is not confined in terms to DRs and considers all realizations (t(218.5)=3.20, p<0.01). Proportionally, the distribution of overt realizations is found to be significantly unequal in both genres, i.e. at least one DR shows a different distribution than the others (χ2(5)=51.838, p<0.0001 for personal narratives; χ2(4)=170.65, p<0.0001 for editorials). Independent measures t-tests between genres for individual DRs are reported in Table 3. These disclose significant differences between the genres for Comment, Continuation, Explanation and Elaboration. All show lower degrees of overtness in editorials than in narratives, with the exception of Elaboration, which is realized more overtly in editorials. Contrast is realized overtly throughout in both genres.

5.2.Degrees of overtness in single-authored and co-constructed data

An independent one-way ANOVA comparing co-constructed editorials and narratives finds that differences between genres in terms of degrees of overtness are also significant in the co-constructed data (F(1,17)=8.13, p<0.05), with the narrative genre showing a higher degree of overtness (64.9%) than the argumentative one (61.4%). This is again confirmed by a weighted independent measures t-test with t(196.36)=−2.69, p<0.01. Proportion tests again provide evidence that the distribution of overt realizations of at least one DR differs from the overall distributions of all others’ in both editorials (χ2(4)=27.122, p<0.0001) and narratives (χ2(5)=25.331, p<0.001).

Table 4 reports the results of t-tests between expected means derived from single-authored data and the means per dyad in co-constructed data; these provide information on whether the degrees of overtness that are found for individual DRs in co-constructed texts correspond to those found in single-authored texts. As in single-authored texts, Contrast is realized overtly in co-constructed datasets throughout. In data for the argumentative genre, mean degrees of overtness for DRs Explanation and Comment in co-constructed texts are comparable to those from single-authored data. For DRs Continuation and Elaboration, however, mean degrees of overtness differ significantly from those expected on the basis of single-authored texts. In the narrative genre, mean degrees of overtness for DRs Continuation, Narration and Explanation in co-constructed texts are comparable to those from single-authored data, but show significant differences with DRs Elaboration and Comment.

5.3.Degrees of overtness and adjacency

Table 5 indicates how degrees of overtness behave across genres and modes of production with respect to adjacent vs. non-adjacent positioning of DUs realizing DRs. Degrees of overtness vary considerably between adjacently and non-adjacently positioned DRs99 in single-authored data of both genres (χ2(1)=64.92, p<0.0001 for editorials; χ2(1)=15.96, p<0.0001 for narratives), with less variation in the co-constructed ones (χ2(1)=1.24, p=0.27 for editorials; χ2(1)=2.05, p=0.15 for narratives).

While the overall proportion of adjacently and non-adjacently positioned DRs is relatively homogeneous across all data (80.3% in argumentative vs. 78.2% in narrative data), genres differ with respect to their preferences for degrees of overtness of DRs in (non-)adjacently positioned DUs. In both adjacently and non-adjacently positioned DRs in narrative data, higher degrees of overtness are encountered than in the argumentative data. In single-authored editorials, overt realization is preferred in adjacently positioned DRs, but dispreferred in non-adjacently positioned DRs. Single-authored narratives always favour overt realizations, with degrees of overtness being higher in adjacently than in non-adjacently positioned DRs. Co-constructed data repeat the overall tendencies of single-authored data, but have lower overall degrees of overtness, except for non-adjacent DRs in editorials, which show a higher degree of overtness in co-constructed than in single-authored data.

While degrees of overtness of adjacent DRs show no remarkable variation based on genre, neither for single-authored nor for co-constructed data, significant genre differences in degrees of overtness are encountered for non-adjacent DRs within single-authored data, with narratives showing significantly stronger preferences than editorials for overt realizations of DRs in non-adjacent position (χ2(1)=8.92, p<0.005). These differences are not discovered with co-constructed texts (χ2(1)=1.17, p=0.28).

5.4.Summary

The results of quantitative analyses of single-authored data reveal systematic differences in the variation of degrees of overtness between editorials and personal narratives: in general, argumentative data yield lower degrees of overtness than narrative data, with differences most noticeable for Comment, Continuation and Explanation, and within adjacently positioned DRs; Elaboration is the only DR with a significantly higher degree of overtness in single-authored editorials.

Comparisons of single-authored texts with co-constructed texts show that joint productions are less overt than the single-authored data, but mirror their overall preferences for the encoding and signalling of DRs: with the exception of Elaboration, all DRs are realized in argumentative data with lower degrees of overtness than in narrative data; Contrast is realized overtly throughout, irrespective of genre. Tests of individual DRs per genre reveal that mean degrees of overtness in co-constructed narratives echo those of single-authored narratives for Contrast, Continuation, Narration and Explanation, but are significantly lower for Elaboration and Comment. Within argumentative data, co-constructed editorials mirror single-authored editorials with respect to the realization of Contrast, Explanation and Comment, but Elaboration is realized significantly less overtly, and Continuation significantly more overtly, than in single-authored texts of a comparable genre.

6.1.Contrast

Whereas all other DRs show variable patterns of realization, Contrast in our data is always realized overtly with non-propositional material, i.e. DCs, metacomments and/or pragmatic word order. Since it is additionally encoded in coherence strands throughout, most prominently in antonymic lexical relations and shifts in temporal continuity, it is overspecified by default. This becomes particularly clear if we take into consideration that in both narrative and argumentative editing-based tasks Contrast is always supplemented with overt signals despite generally being encoded in proposition-anchored coherence strands of the bare DUs.

A typical example is provided in (6), an argumentative sequence from a co-constructed editorial in which the Claim in arg#2/2 is rebutted through arg#2/3. In carrying out their task, the dyad who produced excerpt (6) supplements Contrast, which is encoded in topic and referential continuity (‘London’ – ‘it’), temporal discontinuity (‘was’ – ‘is’) and lexical antonymy (‘dowdy’; ‘stale’ – ‘exciting’), with two overt signals: contrastive DC ‘but’ and two parallel fronted temporal adjuncts and lexical antonyms ‘in the past’ and ‘now’, which additionally encode temporal discontinuity.

Overspecified Contrast may be preferred by argumentative genres for reasons of salience since Contrast, in view of its defining condition of semantic dissimilarity, may take over important argumentative Attack functions like antithesis, realizing Undercut moves, or concession, realizing Rebuttal as in (6). However, the consistent supplementation of coherence strands with overt signals in both editorials and narratives suggests that realization of Contrast is overspecified by default; in other words, its realization is not primarily constrained by the genre, but by its semantics, leading to an overspecified, and thus overt, realization regardless of context.

6.2.Elaboration

Apart from Contrast, Elaboration is the only DR that shows relatively similar degrees of overtness across genres, exhibiting preferences for overt realization in both editorials and narratives, with a slightly higher degree of overtness in editorials. In Elaboration, a DU offers additional information about one of the referents in a preceding DU, making it a fairly prominent DR in argumentative discourse. There, it may be assigned the argumentative functions of adding supportive detail or providing an example, thus correlating with Support moves, or of adding additional detail that may result in the rebuttal of an argument, thus correlating with Rebuttal moves.

In excerpt (7), for instance, Elaboration between 1 and 2 is encoded in mereological topic specification between ‘Hizbullah’ and ‘the Bekaa raid’, temporal/aspectual overlap (‘is’ – ‘may have been’) and various strands of lexical coherence, and signalled overtly with the fronted adverbial ‘as such’, particularizing the role of the Bekaa raid. Within the argumentative sequence, the constraints of the genre guide interlocutors to assign the argumentative function of Support to the pair of DUs related through Elaboration.

Elaboration having similar degrees of overtness across genres may not necessarily be due to its semantics, as with Contrast, but rather to both genres requiring overt signalling of the DR in order to ensure activation of the relevant defining conditions and thus assignment of a DR that introduces a lower level of discourse. In (7), for example, the non-signalling of Elaboration might guide interlocutors to assign the DR Continuation with the argumentative function of “multiple support” [26], that is of DU 1 and 2 realizing two independent arguments on the same level rather than a sequence of Claim and Support move.

Similarly, Elaboration may need to be marked overtly in narrative discourse to ensure the speaker-intended interpretation. This is shown in (8), where adverbial ‘more particularly’ signals the defining condition of topic specification for Elaboration overtly, with narr#5/4 introducing a lower level of discourse rather than keeping the discourse on the same level – a potential interpretation of connectedness of the bare DUs that is reflected in excerpt (9), where the dyad assigned Continuation.

6.3.Continuation

Unlike Elaboration, Continuation, which is defined by topic identity in the DUs it relates, shows differences between the genres under consideration. Whereas the genre of editorial prefers Continuation to be realized implicitly with relatively low degrees of overtness, narratives show a preference for higher degrees of overtness (cf. excerpt (9)). Although Continuation, unlike Contrast, Elaboration or Explanation/Result, does not seem to show any clear co-occurrences with argumentative moves according to Stede et al. [34], its frequent occurrences in our argumentative data suggest that it is nevertheless prominent in argumentation.

The typically implicit realization of Continuation in the argumentative genre is illustrated in excerpt (4), above, and in (10), from a co-constructed text. Although one motivation for Continuation to be realized implicitly in editorials may be the author’s preference for remaining diplomatically unclear (see above), data suggests that the argumentative genre may generally prefer the defining conditions of Continuation to be encoded in coherence strands and lexical material only. An example is shown in (10), where ‘an additional concern’ indexes Continuation, supplementing temporal/aspectual coherence (‘has plummeted’ – ‘has hit’) and lexical coherence strands. On the level of argumentation, the lexical index ‘an additional concern’ fulfils the function of a linguistic indicator for a multiple support structure in which arg#3/12 and arg#3/14 realize independent arguments for the conclusion that British students are losing interest in foreign language learning.

6.4.Explanation/Result and Comment

The preferences of argumentative and narrative genres seem to differ most for Explanation (conflated in our analyses with Result) and Comment. Defined by causal connectivity and temporal order, Explanation and Result express a cause-result relationship between two DUs that may argumentatively function as a sequence of Claim and Support move (Explanation) or of Support move and Claim (Result). Our data suggests a preference of Explanation for implicit realization in the genre of editorial, but for exclusively overt realization in narratives, as illustrated in excerpts (11) and (12), respectively from an argumentative and a narrative context. With referential continuity (‘It’ – ‘Mahmoud Ahmadinejad’) and temporal and aspectual coherence (‘is operating’ – ‘has been conducting’) as the only carriers of defining conditions of Explanation linking DUs 1 and 2, (11) shows an argumentative sequence of Claim and Support and reflects the preferred implicit realization of the DR in the editorials. Explanation in (12), encoded in referential, temporal and aspectual continuity, and is signalled through discourse connective because, reflecting its preferred realization in the narrative data.

Genre-preferential degrees of overtness that are very similar to those of Explanation were encountered for Comment, which is defined by a DU selecting another one as its topic. In argumentative genres, Comment may be assigned the argumentative function of supporting a premise or argument or of concluding. Like Explanation, it strongly favours implicit realization in the editorials, and has a preference for overt realization in the narratives. We assume that the different preferences of narrative and argumentative genre with respect to the overt vs. implicit realization of Explanation and Comment arise from genre-specific expectations and their respective inferential schemata [19].

In narrative discourse, interlocutors by default consider a sequence of DUs as representing temporally unfolding events that are linked through the DR Narration; DRs that indicate deviations from this narrative sequence, such as Comment and Explanation, thus require overt marking, and lead throughout our data to significantly higher degrees of overtness for these DRs in narrative texts in comparison to argumentative texts. In argumentative discourse, on the other hand, interlocutors are prone to producing/interpreting sequences of DUs as being linked causally (rather than temporally or continuatively, for instance). For this reason, it seems redundant to signal DRs such as Explanation or Comment fulfilling argumentative functions of Support overtly in argumentative discourse.

6.5.Adjacency

The impact of genre-specific constraints and expectations for argumentative and narrative discourse with respect to the linguistic realization of DRs and their processing is also reflected in the preference for significantly higher degrees of overtness in the realization of non-adjacently positioned DRs in narrative data as compared to argumentative data: we assume that for personal narratives, non-adjacently positioned DUs realizing DRs prefer overt realization because deviations from the default chronological story line need to be accounted for. The fact that editorials appear to prefer significantly lower degrees of overtness in the realization of non-adjacent DRs, on the other hand, may indicate that the constraints of argumentative discourse guide interlocutors to expect arguments and their constitutive units to not be linearized in a straightforward manner; if lower levels of argumentation are introduced within the argumentative sequence, for instance by Elaboration and Explanation/Result, the overt signalling of these DRs thus may be considered redundant.

6.6.Summary

Overall, the systematic variation in the overt vs. implicit realization of DRs appears to be influenced mainly by (1) the semantics of DRs, leading to default realizations irrespective of genre, as is the case with Contrast, and (2) genre, leading to genre-preferential degrees of overtness, as is the case with Explanation/Result, Comment, Continuation and Elaboration. Genre-preferential degrees of overtness in the data seem to result from the production and interpretation of DRs being constrained by genres and their inferential schemata, which specify the typical ways for the encoding and signalling of DRs in context that interlocutors may act in accordance or disaccordance with, as is reflected in genre-internal and participant-specific variation.

For the argumentative genre of editorial, the following constraints for the production and interpretation of DRs seem to hold: because the constraints of argumentation guide interlocutors to produce and interpret sequences of DUs as being linked causally, Continuation, Explanation/Result and Comment do not need to be signalled overtly unless a particular argumentative goal is intended at a particular stage in the discourse which requires them to be signalled with discourse connectives and/or pragmatic word order. Elaboration, however, requires overt signalling as it introduces a lower level in the argumentation, e.g. to function as Support that further develops an argument, and needs to be distinguished from Continuation, which would keep the argumentation on the same level, e.g. by introducing an independent argument in multiple Support. Contrast is overspecified by default.