Ron
My point was that the player (and his caddy) is the only person who may make any decision about reasonableness. Rule 27-2 of course uses the word 'may'. Again it is entirely upto the player.
Others may give factual information and the player may use his discretion about what weight he gives it.
An opponent may of course register a 2-5 claim or a FC may report any possible infringement. But in the end is is down to the committee and the player to sort out.

Incidentally, who said golf was fair

HI DOUG,
I take your point on consensus. We actually agree, only we call it by a different name.

I am, however, rather pleased with the tacit agreement of a player being allowed to play a PB.

Always good to hear from you.

Regards, Ron.

IMO consensus is not relevant to the discussion. However, I see no reason why a player may not ask his marker or FCs their opinion on e.g. whether they think there is RE that a ball is lost in a WH. Ultimately it is up to the player to decide there and then what he is going to do and if the matter is later referred to the committee then it is up to the committee to decide. In reaching its decision, the committee might ask the opinion of all those who were present. Therefore, I would argue that it is in player's best interests to know the opinion of his marker/FCs before he gets to the committee. In this case I don’t think it is asking for advice to say something along the lines of “Do you think that my ball is in the water hazard?”

I mentioned the Paramore vs. Ballesteros situation because here was a situation that required reasonable evidence. They would have been looking for animal droppings or something like that to support Seve’s claim for free relief. Again, the rules do not require a player to consult FCs on this but should the situation come to the attention of the committee then it’s best to get the opinion of those you are playing with. Seve could get an irreversible ruling there and then. That is the luxury of professional golf.

Going back to my personal situation, after I had played my tee shot I was 95% sure my ball was in the LWH behind the green. This left 5% chance of the ball being outside the water hazard (I don't think it would have been lost outside the water hazard but let us say for the sake of argument that it could have been and that I have proceeded with D27-2c/1 in mind).
What happened next was that I played a 'provisional' from the tee and it finished in another LWH. At this point it would obviously be to my advantage to say that the OB is lost in the first LWH so that I could drop by that WH for two. However, what if the provisional ball had landed in the hole? Have I scored a 3 if I go and pick the PB out of the hole? Given that there is a 95% chance that my OB is actually in the LWH behind the green I don't think it would be fair to do that. IMO I can't expect to be able to take a provisional ball in this situation and then proceed based on whether or not I like the position of that PB once played, particularly because it is 19:1 that the OB is in the LWH behind the green. This is why I think D27-2c/1 is not always appropriate.

DC

The rules are clear.

If there is a chance that the ball may be lost outside a hazard, then a provisional may be played.

If, having arrived at the area, there is reasonable evidence that the original ball lodged in a hazard, the player must proceed under Rule 26.

If not, the player may proceed with the provisional. If it's in the hole, good luck to him.