In reply to Michael Gordon:
> That doesn't make any sense to me. Bold 4b usually gets VS and bold 4c usually gets HVS. Sounds as though you're just talking about badly graded routes.
There just aren't enough grades that VS can realistically have to accurately indicate the danger grade. With the exception of silly routes, VS can only take 4b, 4c or 5a. A safe VS can reasonably take any of these values: 4b if it is very pumpy/sustained, 4c normally, 5a if well-protected (but can still be sustained at the grade - see Lost Horizon!). A bold VS would normally be 4b although some soft VS 4c might be a bit bold. You can't know if a VS 4b or 4c route is bold from the grade alone; in my (limited) experience a VS which is bold will be given 4b. In other words, the tech grade is used to indicate the danger rather than the actual tech grade of the hardest move...
> "It also solves the problem of when you put a VS 4b on top of a HS 4c, which logically is VS 4c but with boldness of a VS 4b..."
> The description usually solves that problem. I don't see how the other way does though - without a description you still are no wiser as to whether the hardest moves are the bold ones or not.
The danger grade would tell you. If you have bold 4b (4c) moves on a 'VS', then danger grade would be medium (high). If you have safe 4c moves but some sketchy 3a moves, the danger grade is low. 'Danger' is precisely the feeling of boldness of a route.
French grades are the best predictor of whether or not you will get up a route.
Tech grades give you some warning of whether there is a stopper move (but are rubbish at the top and bottom end).
UK adjectival grades tell you whether trying the route is a good idea or not... :P
Danger grades let you choose the scale of your own adventure.