Inevitably the person you're talking to will repeat the same conversation you just had a few minutes earlier. Above all, refrain from pointing this out. Memory lapses are a physical glitch beyond his control, and emphasizing his impairment is likely to make him feel embarrassed or frustrated. Instead, give simple, polite responses (even if they're the same responses you just gave five minutes earlier). Alternately, if appropriate, redirect the conversation -- but if he fixates on getting an answer from you, go ahead and give it. His insistence means the subject is important to him.

An occasional prompt is OK if he's having trouble finding the right word or remembering something -- but tread lightly. Frequent corrections, correcting in a critical or patronizing manner, or showing your disappointment or frustration all eat away at his self-esteem. Responding in these ways just makes him less likely to want to open up and communicate. Use his reactions as your guide. You may just choose to limit corrections to times when it's absolutely necessary.

If you do need to intervene, use "I" statements: "I'm sorry. I'm just having trouble understanding today." Putting the onus on you is far less intimidating than being told, "What do you mean? You're not making sense."