So, first post here, but I just finished Dawnshard (bringing me up to date on all the published cosmere stuff), and I wanted to share my initial thoughts about what the Shard quartets relating to each Dawnshard might be.
I'll explain what speculations I'm taking as axiomatic for this theory, before I get into the weeds:
1. The two unknown shards are pseudo-Wisdom and pseudo-Prudence, based off what I could see in a quick search of the WoBs. This is uncertain, particularly the latter, but these seem like our best current guesses, and I think it's better than treating them as total unknowns.
2. Taking Nikli at face value, the Dawnshards are the four primal commands used to create the Cosmere. Based on this I do not think there is a Dawnshard of "Destruction". It overlaps too much with Change, and I don't really see any need for it during the process of creation if you have Change as well.
So with that out of the way, onto the 4 Shard Quartets:
Dawnshard of Creation (Command: Be)
Shards: Invention, Whimsy, Endowment, Autonomy.
I think Invention and Whimsy both represent different approaches to creativity, whilst Autonomy allows for the creation of new, separate individuals, and Endowment allows for the gifting of life/investiture/probably other things.
Dawnshard of Change (Command: Change/Improve/Progress)
Shards: Ruin, Cultivation, Preservation, Ambition
It always struck me in Mistborn Era 1 that Ruin and Preservation aren't really opposites. If one wants stasis and the other wants destruction then the outcome is, eventually, going to be destruction, if the contest is even. Ruin and Cultivation, however, are opposites, as well as being complementary. Cycle of life and death and all that. If you add in the influence of Preservation I think you end up with a dynamic equilibrium: things are changing constantly at the micro level but at the macro level things are actually very stable. So the fourth shard's Intent for this quartet needs to be Ambition in order to explain Rsyn's feeling that the Dawnshard of change is "the will of a god to remake things, to demand they be better". I considered Whimsy for this but decided that didn't fit as well with the "be better" aspect.
Dawnshard of Personality (Command: Think and Feel)
Shards: Honor, Wisdom, Odium, Mercy
Less sure about the name/command for this Dawnshard, so feel free to suggest alternatives. The reasoning for this group of Shards by Intent was that they all symbolise internal qualities or principles rather than external ones. To put it another way, I think these are all explanations for why someone acts in a certain way, what motivates them and how they think, rather than simple descriptors of their actions, which I think is what separates them from the next group.
Dawnshard of Behaviour(Command: Act)
Shards: Valor, Prudence, Devotion, Dominion
Again, unsure of what to call this Dawnshard, but I've grouped these intents together because I think these are all more external behaviours than internal mindsets/motivations. They prescribe specific actions (fight, hide/retreat, submit, conquer) regardless of circumstances. Retreating is always against valour even if it is the honourable thing to do in a situation.
So, that's my current theory! Let me know what you guys think- am I missing something obvious? Is this already considered established? Do you mostly agree but think I've got one or more small details wrong?