[kaoD]

And that is wrong AFAICT. PoW is what achieves Byzantine fault tolerance, not the blockchain.

What blockchain achieves is proof of history given only the latest block's hash. This might or might not have a PoW on top of it to achieve BFT.

Practical example:

An authoritative server which responds only with the latest block's hash (this is cheap, think microcontroller cheap) is another way to make a blockchain useful with no BFT. This way blockchain distribution can be offloaded to untrusted peers while the actual agreement is not distributed (and thus no DFT is involved).

EDIT:

Off the top of my head I can see a few applications of such an scheme: imagine a very low-power device taking mission-critical measurements. This device would periodically distribute a message consisting of (current block of measurements + previous message's hash) to untrusted high-power-large-storage clients. In case of any client desynchronizing it can request from its peers the measurement chain, and only has to receive the latest message from the low-power device to ensure the chain he got has not been tampered with.

That is not BFT because the source of truth is just an authoritative server. There is no distributed consensus even if there is distributed storage.

[lmm]

This is just semantics. "Blockchain" in the sense it's usually used means proof-of-work; hashing that incorporates the history tree predates blockchain and exists in things we wouldn't usually consider "blockchain", e.g. git.

[kaoD]

It's unsurprising that discussig what a term means is just semantics ;)

Git is not a blockchain (it's a DAG) but that misses the point: I think the term could perfectly be retrofitted if it was the case. Things predating a term don't invalidate the new term convering them.

Either way I disagree with your opinion and there's nothing to argue further that would change either of our minds.