Why would it always be possible to decompose random variables to allow for a natural latent?
Well, I suppose I overstated it a bit by saying “always”; you can certainly imagine artificial setups where the mutual information between a bunch of variables is zero. In practice, however, everything in the world is correlated with everything else, so in a real-world setting you’ll likely find such a decomposition always, or almost always.
And why would just extracting said mutual information be useless?
Well, not useless as such – it’s a useful formalism – but it would basically skip everything John and David’s post is describing. Crucially, it won’t uniquely determine whether a specific set of objects represents a well-abstracting category.
The abstraction-finding algorithm should be able to successfully abstract over data if and only if the underlying data actually correspond to some abstraction. If it can abstract over anything, however – any arbitrary bunch of objects – then whatever it is doing, it’s not finding “abstractions”. It may still be useful, but it’s not what we’re looking for here.
Concrete example: if we feed our algorithm 1000 examples of trees, it should output the “tree” abstraction. If we feed our algorithm 200 examples each of car tires, trees, hydrogen atoms, wallpapers, and continental-philosophy papers, it shouldn’t actually find some abstraction which all of these objects are instances of. But as per the everything-is-correlated argument above, they likely have non-zero mutual information, so the naive “find a decomposition for which there’s a natural latent” algorithm would fail to output nothing.
More broadly: We’re looking for a “true name” of abstractions, and mutual information is sort-of related, but also clearly not precisely it.
You can generalize mutual information to N variables: interaction information.
Well, I suppose I overstated it a bit by saying “always”; you can certainly imagine artificial setups where the mutual information between a bunch of variables is zero. In practice, however, everything in the world is correlated with everything else, so in a real-world setting you’ll likely find such a decomposition always, or almost always.
Well, not useless as such – it’s a useful formalism – but it would basically skip everything John and David’s post is describing. Crucially, it won’t uniquely determine whether a specific set of objects represents a well-abstracting category.
The abstraction-finding algorithm should be able to successfully abstract over data if and only if the underlying data actually correspond to some abstraction. If it can abstract over anything, however – any arbitrary bunch of objects – then whatever it is doing, it’s not finding “abstractions”. It may still be useful, but it’s not what we’re looking for here.
Concrete example: if we feed our algorithm 1000 examples of trees, it should output the “tree” abstraction. If we feed our algorithm 200 examples each of car tires, trees, hydrogen atoms, wallpapers, and continental-philosophy papers, it shouldn’t actually find some abstraction which all of these objects are instances of. But as per the everything-is-correlated argument above, they likely have non-zero mutual information, so the naive “find a decomposition for which there’s a natural latent” algorithm would fail to output nothing.
More broadly: We’re looking for a “true name” of abstractions, and mutual information is sort-of related, but also clearly not precisely it.