You could start working together and agree that both of you can split up after two or three months, both of you retaining the right to keep working on the idea.
If you do split up, it probably means your ex-partner wasn't that great, so he won't pose any real competition for you.
But most big projects start as successful small projects (e.g. Twitter, Facebook, etc.). So you can't really set out to start something small just to test the waters. You'll either drown or you won't.
"But most big projects start as successful small projects (e.g. Twitter, Facebook, etc.)"
Do you have a source for this?
With small projects you can a) severely limit scope b) enter a smaller market and c) define success in an accessible way.
Edit: Also, with your experiences (from spending 6 months getting to know someone or with your previous business with nterface guys,) it sounds like you were doing some sort of "small projects" with your future cofounders, even if it wasn't framed as such.
Well especially with the example of Twitter, it started as a small little internal tool inside the company. It was a small project that engineers were just doing in their spare time. So that's one example. Facebook too from what I've read. Facebook was just a little stalking like tool Mark created with his friends for Harvard kids. I'm sure when they started they never saw a real scope outside of that. Both of these small projects grew into large projects, because of their success. What I'm trying to say is that you typically can't set out to create just a small project.
The nterface story was definitely just the next level of luck based co-founders. Although, we really did meet by chance. I probably should have gone into more detail that I did in fact hire Dave and Jason to design/program a small project that I was working on. I contracted them out rather than chose them to be my co-founders. It then evolved into something more.
What I'm stressing more in the article is that luck plays a huge role for first time entrepreneurs: smaller network, less experience, can only find people with similar experience, etc.
