Abstract The data from PI are surveyed and classified. It is shown that there is a systematic contrast between the use of single and double quotation-marks; also that single quotes are regularly used to mean ‘in a certain sense’ or ‘in a special sense’. These points, though hitherto neglected, bear on the interpretation of many of W ∗'s most well-known remarks. New interpretations are worked out for four of them: §§101, 122, 202, and 580. Suggestions are made for further research.