Once again, Kundera writes as a teacher of writing in his narrative. As he names a particular bowler hat as a "motif" he explains how it comes to take on meaning. While we are not left to discover the hat’s significance for ourselves, Kundera flips the tables to use it to delve into the background of the characters, in essence, going back in time rather than forward to develop the story.
The lingerie enhanced the charm of her femininity while the hard masculine hat denied it, violated and ridiculed it. The fact that Tomas stood beside her fully dressed meant that the essence of what they both saw was far from good clean fun (if it had been fun he was after, he, too, would have had to strip and don a bowler hat)… (p. 87)
Then Kundera goes on to explain what the hat meant to its owner, Sabina, the mistress of Tomas:
First, it was a vague reminder of a forgotten grandfather (…)
Second, it was a memento of her father.
Third, it was a prop for her love games with Tomas.
Fourth, it was a sign of her originality, which she consciously cultivated.
Fifth, now that she was abroad, the hat was a sentimental object. When she went to visit Tomas in Zurich, she took it along and had it on her head when he opened the hotel-room door. But then something she had not reckoned with happened: the hat, no longer jaunty or sexy, turned into a monument to time past. (p. 87)
Kundera then clearly states that "The bowler hat was a motif in the musical composition that was Sabina’s life." While the hat took on additional meanings with use and time, its accumulated meanings, or representations, became part of the whole. We are, in other words, what we have been. In Kundera’s continued reference to "composition," these parts may be considered stanzas perhaps, all nice snatches of song or blends of notes in themselves, yet that would take them out of context of the complete work.
This next part bothers me a bit; though I suppose it wouldn’t if I’d’ve read this novel decades ago:
While people are fairly young and the musical composition of their lives is still in its opening bars, they can go about writing it together and sharing motifs (the way Tomas and Sabina exchanged the motif of the bowler hat), but if they meet when they are older, like Franz and Sabina, their musical compositions are more or less complete, and every motif, every object, every word means something different to each of them. (p. 88)
I myself had gotten married for the first time rather late in life and can understand what Kundera is stating here. However, I might disagree that the composition has been completed; the memories are shared, thus both parties are adding the meanings of the other to their own repertoire, and new meanings are adding new life to the composition as well. It becomes a collaboration, perhaps; something that Sabina may be unwilling, rather than unable, to undertake with Franz.