Last Sunday I climbed up to Rifugio Coca. My hiking companions were busy with other things over the weekend, but I was undeterred and set out by myself. I had even thought of leaving on Saturday and sleeping at the hut at nearly 1900 m
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In the paragraph above, would it be possible to use Sunday for Last Sunday? What about on Sunday or this Sunday (I think this would be next Sunday, wouldn't it?).
Same thing about on Saturday, I expect I can't leave out the preposition on, can I?
And if I said this weekend (meaning last w/e), would it be right?
Whether "Sunday" means "last Sunday" is a moving target. On Monday saying "Sunday, I ..." it is usually clear that you mean last Sunday. Later in the week, it can start to become more confusing.
Likewise, "this Sunday" and "next Sunday" can be the same, or not. On Saturday or Friday, saying "next Sunday" would probably mean more than a week away, not a day or two.
But earlier in the week, this and next Sunday usually mean the same.
The "on" of "on Saturday" is not strictly necessary, but it sounds better to me that way.