"Etymologiae" presents in abbreviated form much of that part of the learning of antiquity that Christians thought worth preserving. Etymologies, often very far-fetched, form the subject of just one of the encyclopedia's twenty books (Book X), but perceived linguistic similarities permeate the work. An idea of the quality of Isidore's etymological knowledge is given by Peter Jones: "Now we know most of his derivations are total nonsense (eg, he derives baculus, 'walking-stick', from Bacchus, god of drink, because you need one to walk straight after sinking a few)".