I agree with many posters here, that the Shardblades (in use during WoK) have an evil feel. I wonder if they aren't - metaphorically - a two-edged sword, that gives an advantage in battle, but leaves the bearer open to evil somehow - like maybe, the more you use it, the more arrogant and hostile you become. If a person had great stength of character within themselves, they could fend off this evil influence longer than others. I wonder if it's not a coincidence that the Alethi nobles prize Shardblades so much, and have such character problems - the influence to evil would be both cause and effect.
Hmmm - What if the Knights Radiant gave up the Shardblades because they were evil, or had somehow become a conduit for evil?
Or - What if the Shardblades were immune to evil during the Oathpact, but once that was broken, Odium began to be able to work through them somehow?
Re: the Dawnshards - I wonder if these aren't actual shards - broken pieces of something, like if a huge crystal got broken. [Confess that I'm thinking of "The Dark Crystal" ... where are the Gelflings? ]
My theory is that they were corrupted by the KR abandoning their duty and the subsequent use of the Blades for selfish ends, you will note that the glow to the Blades faded away as the people started using them to slaughter each other.
Also suspect that the corruption amplifies the Thrill that the Alethi feel....
I partially agree with these statements...
My feeling is that an "honorblade" is just a shardblade that is wielded by a person with honor, possibly only those who are held to a specific oath (think Kaladin's improved surgebinding abilities after saying the first ideal of the KR). The difference between an "honorblade" and most of the shardblades we see in WoKs is the presence or lack of a binding oath (which seems to manifest itself by a glow). Szeth's shardblade is different, not because of its size, but because he follows a code of honor, possibly with a certain spoken oath that refers to the KR.
As I was writing this, another thought came to me: it might be that only the KR, or rather, people with innate binding abilities (surgebinding, soulcasting sans soulcaster, other abilites that we don't know of yet)
AND say (and keep) the oath can have the "honorblades" we see in the Almighty's messages; might be one of the reasons that the KR in the highstorm vision says that Dalinar "might not be able to join the Knights themselves but he could still fight as a member of the army." (Hurrah for paraphrasing!) The required oath is there because there are a few characters with shardblades that are binders of some sort but whose weapons do not show the characteristics of "honorblades," namely Shallan (though we never see her blade) and Elhokar.
For me, anything that is prefaced with "Dawn" refers to the Heralds, i.e. Dawncities, Dawnchant, Dawnshards, etc. I'll need to reread through WoK to get the specific page numbers but my thought pattern went thus (and it may be a little flimsy, logically):
Kaladin says that his father liked the Heralds because they brought healing to the people. In a reference by either Shallan, Jasnah or Kasbal (I think it is one of them...maybe it was Hoid's apprentice...) they speak of the creators of the Dawncities as being the bringers of healing (along with some other things, I think poetry and art are also included). While this is the only example I can think of at the moment, I am pretty sure there are a few others that I cannot remember.
IMO the Heralds is just a shortened term for Heralds of the Dawn, or the rise of mankind from the darkness. (Seems to fit to me...though it might be the hidden dramatic in me trying to break free, which I have throughly tried to beat out of myself.
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For the record, I think that the Dawnshards are the Heralds blades.