Frodo at Sammath Naur

[Bombadil]

i think the observation of frodo using the words:

i choose not to do

as a phrase with mutliple meanings is a great one. If Frodo said for example "I have chosen not" this could be taken as his decision, rather than the ring's. This would give a feel of a definitive decision with possible premeditations of his intentions. By saying "I choose not to do" Frodo sounds more like his decision at that moment is undecided and, ultimately, that his fate and actions to come are out of his control. And the following when frodo says

I will not do this deed. The ring is mine.

Is almost like a response to the uncertainty. Those lines would not be necessary if Frodo simply meant he chose to keep the ring...instead the those 2 lines follow, acting as a verification.