Iambs All Around
The iamb is a two-syllable creature, made from gluing a stressed syllable to the back of an unstressed syllable. It makes a daDUM rhythm ("allow" is a great example) and, what's more, it's pretty important to "The Canonization."
In fact, you can hear various strings of daDUMs in every line of the poem, to one extent or another. And these strings tend to repeat from stanza to stanza (though not entirely, as we'll soon see). For example, we have plenty of iambic pentameter on hand, which just indicates that the line contains five iambs (penta- means five). You can hear it in the first line of each of the poem's five nine-lined stanzas. Check it out:
For God's sake hold your tongue, and let me love; (1)
If you go back and read that line out loud, you'll hear a pattern emerge: daDUM, daDUM, daDUM, daDUM, daDUM. Now, as we said, this same pattern recurs in each of the stanza's first line (go ahead and read them now—we'll wait), and it also pops up in the third, fourth, and seventh lines of every stanza. There are exceptions, though:
Or the king's real, or his stamp'd face (7)
Even if you were to give those words different emphases, we only have eight total syllables to go on, so it's a far cry from the ten syllables of the regular iambic pentameter. So why break the pattern? Well, given that this poem is framed as a conversation between the speaker and an unnamed second person, it really wouldn't sound very natural to have a lock-step meter all the way through. Breaking the rhythm of the lines up makes this poem sound more conversational.
Donne does this at other times, as well. The second, fifth, sixth, and seventh lines are all in iambic tetrameter, using four iambs as opposed to five. Here's an example:
Or chide my palsy, or my gout; (2)
You should hear one less daDUM if you read that line out loud, and the same goes for the other second, fifth, sixth, and seventh lines in each of these stanzas. Again, though, there are exceptions:
Contemplate; what you will, approve, (8)
Here the line has the right number of syllables for a line of iambic tetrameter (eight), but it's really hard to cram "Contemplate" into iambs. It would sound like "contemplate," which is just…odd. That's okay, though, because remember that these little breaks in the poem's metrical patterns help it to sound more conversational. To return to a regular rhythm, Donne tacks on a line of iambic trimeter (three iambs) in the final line of each stanza.
Finally, we should mention the poem's rhyme scheme: ABBACCCAA. That is, each letter represents that line's end rhyme. Unlike the varying meter of the poem's lines, you can count on this scheme to hold up throughout the poem. After all, this is about two lovers finding harmony in one another, and what better sonic technique to get that idea across than some good, old-fashioned rhyme?