Can’t remember the source, but for some reason it sticks.

Stun, to me indicates a situation where the person concerned was unable to show any reaction (at least momentarily), whereas Astound or astonish indicates a surprise which is also accompanied by an approrpriate (and perhaps exaggerated) reaction.

I would like to know how valid and correct this observation is.

About being stunned at news. Being stunned by a hammer would be similar to being “stoned” as in the sense of being punished by a thrown rock. The hammer would require an action to cause a stun. That is, one might deliver a blow using a hammer to make the blow more intense (than, say, a bare hand or stalk of celery); the blow would then be the cause of the stun. Such a stun would be more intense than a distraction. The recipient of such a blow would be incapable of thought for measurable seconds or longer. Stun implies a state more active than unconscious, yet absent of constructive or directed thought.

Being stunned by a hammer would overlook the details of the hammer being acted upon, the resulting blow, and the fact that it is the effects of the blow, the impact of the hammer with the recipient, that results in the stunning impact. Presumably the blow would also result in bodily injury, in addition to the stunning effect on the thinking processes.

A stun to the thinking processes resulting from observing something, or hearing some information, though, might not be the result of another’s actions. I could imagine that the stun to thinking processes would be at the existence of an external factor, rather than by the action of an external factor or person.

Should grammar and philosophy tend to agree? Should the correctness of “stunned at” or “stunned by” be related to whether the cause is a metaphorical or physical action, or whether the cause is a discovery of something intense and surprising? Or am I lost in the information density of the poetical and in subtle intimations again?

May I be permitted to think the degree of disruption of the thinking process described as a stun as similar to the result of stoning? Then I would posit astonishment and astoundment to be a lesser degree of disruption to the thinking process. That is, astonish implies a major distraction of thought, as one’s attention is caught by beauty, by immensity of scope, or surprising juxtaposition of one’s surroundings and companions. Astound would be closer to stunned – a mild disruption of the train of thought just a bit more intense than mere distraction.

As you point out, anything less dramatic than a person lying disoriented on the floor would be using these terms to perfect hyperbole.