How did 'even' semantically shift to emphasize something surprising or extreme?

This post's title refers to ODO's definition 1. Used to emphasize something surprising or extreme.

[ OED : ]  II. In weakened use as an intensive or emphatic particle. (In later use many uses of senses in this branch show some suggestion of sense A. 8.)

5. Exactly, precisely, just. In later use generally somewhat archaic.

8. a. Used to convey that what is being referred to is an extreme case in comparison with a weaker or more general one which is stated or implied in the adjacent context. Prefixed to the particular word, phrase, or clause in which the extremeness of the case is expressed.

 b. In uses parallel to those at A. 8a, but placed after the word, phrase, or clause to which it relates.

[ Etymonline : ]   The adverb is Old English efne "exactly, just, likewise." Modern adverbial sense (introducing an extreme case of something more generally implied) seems to have arisen 16c. from use of the word to emphasize identity ("Who, me?" "Even you").

Etymologists are uncertain whether the original sense was "level" or "alike."

Q1. What semantic notions underlie 'levelness' or 'alikeness', with 'something surprising or extreme'?

Q2. Don't the semantic notions of 'levelness' or 'alikeness' contradict the notion of 'something surprising or extreme'? If X is more extreme than Y, then X and Y are neither level nor alike.

Solution 1:

I will try to explain the underlying semantic notion that connects sense (6) to sense (9). It's speculative, but I think on the right track.

Consider:

1. She's mean, evil even.
2. She's mean. She's even evil.

I take it that these are the kinds of construction you're asking about. Here, even intimates a more extreme version of mean, licensing evil.

A rough paraphrase of these would be:

3. She's mean, or, more exactly, evil.

or

4. She's mean, or, more precisely, evil.

These paraphrases include the words exactly and precisely. This is essentially sense (6) of your definition. The idea is that the new, more extreme word (in this case evil), is more exact or precise than its antecedent (in this case mean).

This should help you see how to get from sense (6) to (9). That this is the correct link to be looking for is corroborated by your quote, which says that sense (6) "suggests some notion of sense (9)."

Solution 2:

Even is a scalar focus particle: the exact meaning is not only one of "surprise," but there is also a comparative component. It almost always implies that something is more unexpected than some understood reference point. So when you say:

Even Thomas came to the party.
I even helped her find a new roommate.
I didn't even put on a belt, I was in such a rush.

It implies that others, generally more inclined to attend the party, also came; or that you did other, less helpful things to assist with her living situation; or that there were other, less remarkable indicators of your haste.

Heine and Kuteva (World Lexicon of Grammaticalization) give examples of words meaning "resemble" in Chinese and Colloquial German grammaticalizing to a comparative marker. Could this be a similar phenomenon? Not sure. I think even is an interesting word because the precise meaning is often not well characterized.