In the Valley of Sound, Juster ties Milo's lesson on perspective from Dischord and Dynne to the larger theme of appreciating everyday life. Just as Milo fails to appreciate the beauty of noises, the doctor and his sidekick are unable to appreciate the nicer sounds. When he reaches the Valley of Sound, Milo learns what happens when too many people take Dr. Dischord's perspective. Just like Milo and Dischord, the residents of this valley have an unbalanced appreciation of sounds—they seem to prefer one kind to the extreme. As Milo learns, the residents of the valley became so unable to appreciate beautiful sounds that the Soundkeeper takes them away along with all the noises as well. Notice the plot similarity here with the city of Reality, whose city disappeared because they failed to appreciate it. It seems that what people take for granted in the Lands Beyond disappears.
At the Soundkeeper's fortress, Milo learns about sounds in much the same way he learned about words in Dictionopolis. Sounds become tangible just like words at the Royal Banquet or in the word market. When he is actually able to see sounds in their "true" forms and the elaborate catalogue system that the Soundkeeper uses to keep track of them all, Milo seems to gain a greater appreciation of both noises and nice sounds. When Milo catches the word "but" in his mouth, Juster returns to his motif of punning by playing off the popular expression "on the tip of his tongue." Once the sounds have been restored, the Soundkeeper realizes that her inability to appreciate all sounds makes her just as bad as Dischord and Dynne. Beauty, as we learned in the last section, is a matter of perspective. The Soundkeeper realizes the sense of this, referring to Rhyme and Reason, symbols of wisdom, and declares that she will try to use each sound at the right time.
Milo learns a second lesson in this section during his detour to the island of Conclusions. Once they pass through the Valley of Sound, Milo and his companions each makes a statement that demonstrates an assumption. They make decisions without having enough information to do so and end up literally jumping to Conclusions. Since he got to Conclusions by deciding something before having enough information, it is fitting that Milo must swim through the Sea of Knowledge to get back to shore. When he finally makes it to the beach, Milo finds himself drenched in the waters of knowledge while the Humbug, who seems to be more interested in sounding knowledgeable than actually being knowledgeable, is bone dry. Juster seems to be telling us that one has to be open to knowledge in order to absorb it.