There are several English constructions in which a certain constituent appears to the left of its canonical position, typically sentence-initially, leaving its canonical position empty. Such constructions involve Left-dislocation and Y-movement. These operations are called ‘Preposing.’ The preposed constituent of such constructions is generally regarded as the topic of the sentence which involves that constituent. Topics must have at least two features; ‘aboutness’ and ‘givenness.’ The feature ‘aboutness’ defines the range of comment, and the feature ‘givenness’ means ‘informationally old or given.’ The purpose of this paper is to show that the function of Preposing is to reinforce the aboutness of the preposed constituent of a sentence and that most preposed constituents have givenness. We examined Preposing for this purpose. Tough-movement and Passivization were examined also, because they have characteristics informationally similar to those of Preposing.