The difference is that the author was aware of that grant at the time they contributed the code since it was implicit in the license. CLAs are often essentially a way to backdoor additional grants after the fact without the original author's permission.

How so? If anything the CLAs I've seen are much more explicit that your code may be distributed as part of a future closed-source version of the project than, say, the MIT license is.

With all of the well-known open source licenses, it's generally clear to the author up front what rights they are granting. With CLAs they are usually fuzzy by design: maybe the rights will be used to go closed source, maybe to sue anther entity, etc. (it generally depends on what's in the best interest of the entity who wrote the CLA) Sure, they're explicit in the sense that they say 'we can do pretty much anything we want down the road' because they have to... that's the point of the CLA: to grant the authoring entity the right to make decisions down the road without consulting those who contributed. Oracle is practically a textbook example of why this is usually a bad thing for developers/users.

> With all of the well-known open source licenses, it's generally clear to the author up front what rights they are granting. With CLAs they are usually fuzzy by design

Not my experience at all.

> Oracle is practically a textbook example of why this is usually a bad thing for developers/users.

What would have happened differently there if people had contributed under an MIT license instead of signing a CLA?