Ode
Let's take a little trip back in time. The ode is an ancient Greek form of poetry that is a formal, dignified form generally written in praise of or in defense of a particular person or thing. Keats's "Ode on Melancholy" certainly qualifies—his poem is written in a formal way, with a tight rhyme and meter, and it argues that melancholy is a good thing. You can only experience joy and pleasure, argues the speaker, by allowing yourself to experience melancholy and anguish, as well. Joy and pain are linked.
That's the basics of the ode. Now for the nitty-gritty details. What about the rhyme and meter? Well, the poem is broken into 3 stanzas of 10 lines each. So far, so good. But the rhyme scheme is a bit quirky. The first two stanzas follow a rigid pattern: ABABCDECDE. So the first four lines of the poem stand apart in terms of the rhyme scheme, and the final six lines do their own thing, too.
Then the final stanza shakes it up a bit. Although it also opens with ABAB, the final six lines are mixed up. It ends with CDEDCE. Keats's most famous ode, the "Ode on a Grecian Urn" shakes up rhyme scheme in the final six lines, as well.
So here's a two-parted question for a brave Shmooper to tackle: first, how do the first four lines stand apart from the final six lines in each stanza in terms of the theme or message of those lines? And second, why would Keats mess around with the rhyme scheme in the final six lines of the last stanza? What's the effect of that? (And yes, you can assume he did it on purpose.)
Metrical Matters
Now let's tackle the meter of the poem, which is a fancy way of describing the pattern of stressed and unstressed syllables. This poem, like many of Keats's odes, is written in iambic pentameter.
We'll translate: iambic refers to the particular pattern of stressed and unstressed syllables. An iamb is an unstressed syllable followed by a stressed syllable: daDUM. Pentameter tells us that there are five ("penta-") of those iambs per line. Let's check it out in action—we'll highlight the syllables that you'd naturally stress when reading this out loud:
Then glut thy sorrow on a morning rose (15)
There you have it: daDUM daDUM daDUM daDUM daDUM. Five iambs. Iambic pentameter.
Most of the poem is fairly regular in its iambic pentameter, although there are some notable exceptions where Keats mixes things up for effect. For the most part, you don't even hear the meter unless you're looking for it (some critics have argued that iambic meter sounds most like natural English conversation), so those places where Keats breaks the meter really do stand out unexpectedly. For example, in line 12, the first iamb is reversed:
Sudden from heaven like a weeping cloud
This is called a trochaic substitution. It seems to emphasize the suddenness of the onset of a melancholic mood—this line smacks you in the face with the inverted first foot right up front before gliding back into that more conversational iambic pattern. How cool is that? What other breaks in the meter can you find, and how do they affect your reading?