* By *adversative result* I mean a real result that is adversative to the inference from foregoing contextual information.
* By *adversative ground* I mean a ground which induces an real result that is adversative to the inference from foregoing contextual information.

I read in Duden the following example for *allein*:

> 
> Ich hoffte auf ihn, **allein** ich wurde bitter enttäuscht.
> 
> 
> 

In this example, *allein* introduces an **adversative result**. 

However, as I read from an old grammar book ([‘Second German Book’](https://archive.org/details/secondgermanboo00fraegoog) by Thomas Kerchever Arnold & J.W. Frädersdorff, published in 1854), *allein* serves to introduce a “real ground” or, equivalently, an “actual cause”, which accounts for WHY the inference from the foregoing contextual information fails to hold, i.e. it should introduce an **adversative ground** instead of an adversative result.

The point made in the grammar work seems to contradict the Duden example. I am wondering which one I should follow and which not:  

Is the point made by that grammar book so out of date that it no longer applies or is the example from Duden not good in style?