Peer review - discussing paper with the author I am currently attending a week-long conference. A few weeks ago, a quite respected professor in my field posted a paper on an online preprint server, making a series of claims, which are quite linked to my own research. In the beginning of the conference I approached him, asking if we could discuss his latest paper. He said yes, but asked if we could maybe wait a couple of days, since he was swamped with tasks during the beginning of the conference.

In the evening, I am discussing this paper with a couple of colleagues over beer. I am quite critical about some of the claims, and I voice my criticism. After the discussion, one of my colleagues pulls me aside. He says that he is currently reviewing the paper for a journal, and since I obviously have strong criticisms, he would like to suggest to the editor that I join the review panel, if I have no objections. I agree, he contacts the editor, and I am now reviewing the paper.

My question is now: Can I still discuss the claims of the paper with the author as we initially agreed upon?

(By the way: I know that my colleague overstepped the line by revealing himself as a reviewer. This is not part of my question.)
The benefits of peer review are first to detect and prevent fraud and ridiculous claims, and second to improve the clarity of the published record. So, in general terms, if your conversation furthers these objectives, it's a beautiful thing.

On the other hand, if formally reviewing the paper comes with a commitment to maintain confidentiality, you will want to reconsider, and think carefully about how you back out of either the conversation or the formal review.

Confidentiality has benefits, like allowing reviewers to be critically honest without fear of retribution. It also has problems, like the inability to have an efficient conversation about honest disagreements and misunderstandings. This handicap is why some journals (along with the preprint system) are starting to allow for conversation without the blinds of confidentiality. If your journal-specific reviewer expectations do not prevent an open conversation, it may be the best approach.