The non-human forces the determine us.

onsider the case where I miss a very short putt and kick myself because I could have holed it. It is not that I should have holed if I had tried: I did try, and missed. It is not that I should have holed it if conditions had been different: that might of course be so, but I am talking about conditions as they precisely were, and asserting that I could have holed it."

In this short paragraph, Austin is making a claim about what it is possible for him to do. In the previous entry, we saw that such statements are characterised by their appeal to possible worlds. So, roughly, what Austin is saying here is that the sentence “Austin holes his putt” is true in at least one possible world within a specified subset (X) of 
possible worlds.
to recap, the concern is that determinism leads inexorably to the view that human beings are mere receptacles through which non-human causal forces exert their powers.