What is the opposite of a "reply"?
Some might say that the "question" is that which you "reply" to. However, when I "post" something I also get "replies". Thus, if I am the reply, is there a general word for the thing that I am the reply to?
To clarify, the gist of what I'm trying to say is something like: "These writings can have pair wise relationships with other writings. In these relationships they can either be the reply or the ________."
Solution 1:
The 'original post' (or opposite) to a reply may be a question, statement, reply, etc. However, what we want is something that describes the original post's function as the inverse (I'll call it a complement) of a reply, rather than the nature of the original post outside the context of a reply.
Motivated by Andrew Leach's comment to the main question, namely
... [that] which prompts the reply ...
I suggest prompt as the complement of reply.
The verb form includes the following definition:
Prompt verb : to say (something that encourages a person to talk) - M-W
Although the noun form is often defined in terms of acting (prompts for actors), the noun prompt can easily and naturally carry the sense of the thing that triggered the reply.
In the context of the OP's sample sentence, we then have:
These writings can have pair wise relationships with other writings. In these relationships they can either be the reply or the prompt.
Solution 2:
What is the opposite of a “reply”?
"These writings can have pair wise relationships with other writings. In these relationships they can either be the reply or the ________."
+1 for a valid question (not sure why others would want to downvote it)
Short answer : there is no specific word for opposite of reply in generalized communication. The best you can get is when you restrict to "questions/queries/requests" for which you get "responses/replies/answers".
Any correct opposite of generalized "reply" is going to be so generalized that it will be almost meaningless : In the most generalize view, action or event is the opposite of a reply or reaction.
Eg, you can reply to a question/query/request. You can also reply to a comment or a greeting. You can also reply to a reply ! You can also reply to an absence of a reply !
Consider this series of exchanges between X & Y & Z, where words in square brackets are informational :
X: Hello All. [ greeting ]
Y: Hello X. [ reply to greeting ? ]
X: I need help on topic ABC. [ not a question ; probably a request ; but surely a simple statement. Is it also a reply to Y ? ]
Y: Go on, I know about ABC. [ reply to request ? statement ? ]
X: Who invented ABC ? [ specific question ]
Y: It was invented by Z in 2013 [ specific reply ]
Z: Do not give wrong information about year of invention ! [ reply ? reaction ? ]
Y: Well, well, well ! I did not know that Z was in this group ! [ reply ? statement ? comment ? ]
X: Hey Z, you invented ABC, but 2013 is wrong. Which is the correct year ? [ specific question ]
.
.
.
.
X: Z, you there ? [ reply to ... what ? reply to absence of reply ? ]
Y: Hey X, given his geographical location, Z is probably sleeping now. You might get a reply tomorrow [ reply from Y, but question was for Z ]
Basically, there can be no logical pairing of [S,reply to S] where you want a word for S.
If the sequence is {S1,reply to S1,S2,reply to S2,...} then even [reply to S1,S2] is also a pairing, hence there can be no specific word for S.
In the most generalized view, every thing can be considered "an action or an event" and the response or the reply is the reaction, which is so generalized that it is almost meaningless.
I hope I have not converted this question into a philosophical issue of semantics, but would be happy to elaborate if any query is raised.
Solution 3:
I'm going to step out of the box and go for:
Request-response pairs as defined for computer communication interchanges.
Request-response.
One of the basic methods computers use to communicate with each other, in which the first computer sends a request for some data and the second computer responds to the request.
While not strictly a linguistic answer I believe this correctly describes the phenomenon you are referring to.
Reference:
https://en.wikipedia.org/wiki/Request%E2%80%93response