If a venue representative passes a hint to some musicians that a free space for jamming is available certain days of the week and certain hours, with some sound equipment and possibly an audience, is that an invitation which obliges them to pay the musicians? Certainly not.
The one thing that makes the context different is if the venue wants very specific musicians, and all of their choices are pros who expect to get paid. The venue can't get any of the musicians it wants without paying and that's that.
If a venue is not picky about musicians, it can easily get free ones. So many free ones that if three of them cancel, it can still call a fourth to come over.
> and all of their choices are pros who expect to get paid
I disagree that an alternative exists. Pay them for their time. They're enriching your business, or at the very least, providing you with their time and expertise.
> If a venue is not picky about musicians, it can easily get free ones
The way you talk about musicians (see also; you "ape" comment earlier) sounds like you don't value them as people.
> They're enriching your business, or at the very least, providing you with their time and expertise.
What? Not necessarily at all. Say I have a bar that is completely dead on a Wednesday night, due to it being Wednesday night and it being in some off part of town.
I could advertise that I have some free jam space for musicians, a drum kit and a PA with a few microphones and maybe some guitar/bass amp or speaker cabinet. Maybe people will show up to make some noise. Those same people (and maybe a few of their friends) will buy a few drinks, and that's where the "enriching my business" part comes in.
Nobody is required to buy a drink, and so this is a better offer than them having to actually rent equipment and room.
The one thing that makes the context different is if the venue wants very specific musicians, and all of their choices are pros who expect to get paid. The venue can't get any of the musicians it wants without paying and that's that.
If a venue is not picky about musicians, it can easily get free ones. So many free ones that if three of them cancel, it can still call a fourth to come over.