"Introduction to Poetry" is written in free verse, meaning the poem does not follow any preset patterns. Admit it, you were thinking "free" in the sense of who would pay for this stuff? We could tell.
But just because this poem's free verse, doesn't mean it's worthless. Really, this form means that the poet is "free" to use any kind of line, stanza, and rhythm that they feel best expresses the feelings and ideas in the poem. So the lines and stanzas are simply left to chance—they're packed with meaningful choices.
Many poets writing in free verse use elements of structure and meter to create emphasis—to point to a feeling or an idea. While these subtle variations may go unnoticed on a first reading, closer inspection shows how they help give the poem greater impact and interest.
Lucky for us, there is a great example of this in "Introduction to Poetry." But first, let's just break this thing down, shall we? It's divided into seven stanzas. Three of the stanzas have two lines (these are called couplets) and three of the stanzas have three lines (called tercets). The lines in these six stanzas are all pretty short, but they do vary somewhat, and they have irregular meters. No fancy feet here.
Now it's time to play a round of Which of These Stanzas is Not Like the Others?
If you answered stanza two, you win the grand prize! Unfortunately, that amounts only to the feeling of pride you get from being correct, and Shmoop's admiration and respect. Good things, but yes, we agree, a car would be better. Stanza 2 is where we find that great example of using structural and metrical elements in a free verse poem. By giving the line its own stanza, Collins is guaranteeing that it gets a lot of attention. The line really stands out on the page—lots of white space around it.
Now that he has our attention, he makes the line stand out from the other lines even more by giving it a regular meter (iambic tetrameter in this case).
Before you say gazundheit and move right along, bear with us for a second. Iambic tetrameter is very much a real thing, and it's actually quite simple.
The regular pattern of stressed and unstressed syllables in the line gives it a very rhythmical feel. It sounds different than the other lines:
or press an ear against its hive
Hear it? It sounds a bit like this: daDUM daDUM daDUM daDUM. Each of those daDUMs is what's called an iamb, and when you have four of them in a row, we call that tetrameter.
And what does this line happen to be about? Sound! Get it? The content, idea, and feeling of the line are emphasized and mirrored by the structural and metrical choices that Collins made.
Pretty cool stuff, right? Well, we think so anyway.