Discourse Theory

The analysis of discourse in written texts aims at understanding the sequential organization of documents. The goal is to track the flow of concepts, and how they relate to each other. Discourse relation theory is a formal description of the possible relationships between events in the text. According to (Asher & Lascarrides, 1995), there are 9 discourse relations or categories: Narration, Elaboration, Continuation, Explanation, Background, Result, Contrast, Evidence and Commentary. The definition of each of these relations is listed below. (The notation (A,B) means that event A precedes event B in the text.)

Discourse Relation Types

Narration(A,B):
The event described in B is a consequence of (but not necessarily caused by) the event described in A:

(1A) Max stood up.
(1B) John greeted him.

Elaboration(A,B):
The event described in B contributes to the occurrence of the culmination of the event described in A, i.e. B's event is part of the preparatory phase of A's:

(2A) The council built the bridge.
(2B) The architect drew up the plans.

Continuation(A,B,C):
If the last 2 events A and B are related by Elaboration, and the current event C is also an Elaboration to A, then it is a Continuation on B; so the current event C is a Continuation:

(2A) The council built the bridge.
(2B) The architect drew up the plans.
(2C) The community paid for part of the bridge construction.

Explanation (A,B):
The event described in clause B caused the event described in clause A:

(3A) Max fell.
(3B) John pushed him.

Background (A,B):
The state described in B is the backdrop or circumstances under which the event A occurred (so the event and state temporally overlap):

(4A) Max opened the door.
(4B) The room was pitch dark.

Result (A,B):
The event described in A caused the event or state described in B:

(5A) Max switched off the light.
(5B) The room was pitch dark.

Note that (5) has similar structure to (4) and yet unlike (4) the event causes the state and the discourse relation is Result. This captures the intuition that if (5A) causes (5B), then (5B) could not have been the case when (5A) happened, therefore, the antecedent of Result is satisfied, but the antecedent to Background is not.

Evidence (A,B):
A is a generic statement, B describes an instance of the antecedent of A.

(6A) The EC has been acting decisively lately.
(6B) Last night's meeting came to an agreement by 8pm.

Contrast (A,B):
There is a discrepancy between events A and B:

(7A) John had a headache.
(7B) But, he didn't take any medicine.

Commentary:
This case is used to label a person's quotes or opinion about an event.

(8A) John and Mary are getting married.
(8B) These are exciting news.

None of the Above:
This case is used to label anything that doesn't belong to the other relations. All the others and their reverse representation have to be analyzed before assigning this label.

Reverse Relations

Language is highly variable, and sometimes the events appear in reverse order for stylistic reasons. This happens particularly often with causal relationships. Therefore, in discourse relation theory, cause and effect and effect and cause each have distinct labels: Result and Explanation. An example of a such a sentence pair is (9). In this order, the relationship is Result. In the reverse order (10), it is Explanation.

(9A) Max was sick.
(9B) He took aspirin.

(10A) Max took aspirin.
(10B) He was sick.

For Elaboration, Background, and Evidence, reversal is less likely but possible. If you encounter such relationships in the text, they should be labeled as Reverse-Elaboration, Reverse-Background, Reverse-Evidence. The other relations, i.e. Narration, Contrast, Continuation and Commentary do not have reverses. An example for Reverse-Elaboration (11), Reverse-Background, (12) and Reverse-Evidence (13) follows.

(11A) The mother bake the cake.
(11B) The kids enjoyed the birthday party.
(12A) It was raining.
(12B) Mary went out for a walk.
(13A) Last night the PTA meeting came to an agreement about kids and guns.
(13B) School officials and parents have been discussing about security issues lately.

Multiple Relations

It is quite common that more than one discourse relation holds between sentences. For example in (5), Result does not conflict with Narration, and so, both Result and Narration relations hold. As another example, consider (10): Sickness explains why Max took the aspirin, and the sentences are related by Explanation. Sickness also describes the circumstances when Max took aspirin, hence the sentences are related by Background as well. All the category labels that apply should be identified in this homework.

REFERENCES:
Asher, N. and Lascarrides, A. (1995). Lexical Disambiguation in a Discourse Context. Journal of Semantics 12:69-108.