Continuing the discussion from The Society's Community "How To" Guides:
Sometimes you may wish to reply to an existing conversation thread, or topic, but in a way that starts a new discussion, or creates a separate post. For example, you might wish to take the conversation in a new direction, or think that this topic should stand out in some way.
To start a new topic, but link to an existing reply / comment, click on the time stamp of that comment. This will bring up several options for sharing content, including a link that says “+ new topic”.
To link to the main topic, instead of clicking on the ‘Reply’ buttons, you should click on the time stamp of the original comment OR scroll to the bottom / end of the thread and click on the ‘Share’ button.
In all cases, clicking this option will start a new topic but also place a link to the original topic at the start of your post which you can either leave at the top, or you can add content above and below it. This will also place a link to this new thread at the end of the original post, for reference.