If you think about it, this book just tells a very limited story: a normally very accurate corrector in a whim changes a 'yes' in an historical study about the 12th century siege of Lisbon into a 'no', and as a consequence his life drastically changes, but not history. It's a brillant idea and Saramago has converted into an entertaining love story. The deeper message is that you can't change history, but you can change your own life if you only take a little risk.
Saramago has turned this story into a very elaborate, ingenious piece of writing, with continuous leaping between present and past, giving the impression that the present seems to influence the past (the corrector writes an alternative history of the siege), but in the end everything turns out the same (the city falls). All this mumbo jumbo is bit too ingenious to my taste. And again Saramago's 'tumbling' writing style (page long sentences full of clauses and commentaries) just isn't my thing. I had this feeling also with the 2 other books of him I've read. But, still, I'll keep trying...
(rating 2.5 stars)