Let's start with the meaning of the word "sonnet." The most basic thing you need to know about the sonnet form is that it refers to a poem in 14 lines. When you think about it, this is a pretty interesting length for a poem. 14 lines is too short to talk about a vast range of topics, but it's long enough to talk about one or two ideas in a fair amount of detail.
In response to these challenges, poets over the centuries have developed some traditional ways of organizing the thought-patterns within sonnets. These patterns usually correspond to a particular form of the sonnet. Because all sonnets have 14 lines (aside from some super-rare varieties), these different forms are defined by their different rhyme schemes. Many poems featured on Shmoop showcase the popular "Italian" or "Petrarchan" variety of sonnet, which falls into two main halves rhyming. (The rhyme scheme looks like this: ABBAABBA CDCDCD, with some room for innovation in the second half. Check out John Donne's "Holy Sonnet 7", William Wordsworth's "London, 1802", and John Milton's sonnet "On His Blindness" for some top-notch explorations of this type of sonnet.)
Of course, our main man Mr. William Shakespeare wrote a type of sonnet with a different rhyme scheme. His brand of sonnet falls into four major sections, with a rhyme scheme of ABAB CDCD EFEF GG. The first three sections are known as quatrains (1-30, and the last section is known as the couplet. Shakespeare wasn't the first to use this type of sonnet. (When the Bard took his turn with the form, the aristocratic poet Sir Philip Sidney had already made it famous with his sequence Astrophel and Stella). Even though Shakespeare didn't invent this type of sonnet, though, he was so good at it that the form is now named after him.
As you can see from the rhyme scheme we just laid out, the Shakespearean sonnet lends itself most naturally to the poet working out a different idea in each of the three quatrains, and then summing everything up in the couplet. Many (if not most) of Shakespeare's sonnets follow exactly this pattern. But isn't there something about mastering a set of rules that makes you want to break it? Shakespeare sure seems to have thought so. As it turns out, Sonnet 75 is one of the poems where the old Shake-meister shows how he got his name—by totally shaking things up.
In this case, we get one basic idea in the first 2 (and arguably 3) lines, as the speaker compares his relationship with his beloved to the friendly interactions between "food" and "life" and "sweet seasoned show'rs" and the "ground." That said, once he introduces the "miser" imagery in line 4 (though it looks like he's already laying the groundwork for it in line 3), he simply can't give it up. In fact, this idea dominates the following section of the poem all the way down to line 12. Lines 13 and 14, the concluding couplet, more or less summarize the same ideas as the miser imagery, only this time they transform the imagery to one of "gluttony" instead. In these ways, Sonnet 75 marks a significant, though subtle departure from Shakespeare's standard operating procedure.
So much for the poem's form. But what about its meter? The meter of Shakespeare's sonnets (and his plays) is the single most common poetic meter in English: the iambic pentameter. This term is definitely a mouthful, but it's not so hard once we break it down. Let's start with the word "pentameter." The "-meter" part is easy: that just means some way of dividing up or measuring (in the sense of a "measure" in music) the words in the poetic line. As for the "penta-" part, that just comes from the Greek word for "five." So a "pentameter" is a line that is divided into five sections or "measures." (Just so you know, these metrical units are normally called "feet." Go figure.)
As for "iambic," that just means that each of those measures, or "feet," is going to follow a certain rhythm, known as an "iamb." An iamb is made up of two syllables: the first syllable is lightly accented and the second syllable is strongly accented, giving the rhythm "da DUM." Thus, a complete poetic line of five iambs sounds like this:
daDUM daDUM daDUM daDUM daDUM
To see this rhythm in action, let's take a sentence we know... How about:
So are you to my thoughts as food to life.
Of course, it would be pretty boring to have every single line of your poem follow the same rhythm. Thus, skilful poets tend to mix things up a bit, for example by taking one of the iambs and replacing it with a "trochee," which is just the same thing except that the stressed and unstressed syllables are reversed: "DA dum." Sometimes seeing where the rhythm has flipped is a matter of interpretation. In our interpretation of the poem, the first iambic foot of line 6 is flipped into a trochee, giving us the following rhythm:
Doubting the filching age will steal his treasure.
Did you notice anything else interesting, or out of the ordinary about this line? How about the fact that it has an extra, eleventh syllable tacked on at the end? In fact, it's totally legit to have an extra eleventh syllable, so long as this syllable is unstressed. By tradition, this rhythm at the end of a line is called a "feminine" ending. When the line simply ends with the tenth, stressed syllable, this is known as a "masculine" ending. These terms don't really have anything to do with gender (you're free to speculate about why they are called what they are). They're just the traditional names to refer to this rhythmical phenomenon.
Now, you may wonder why Willy S. decides to vary his pretty constant rhythm with a feminine ending here. And we might say, "Good question, chums!" Reading this line, we're thrown slightly off a bit of the poem's rhythmic momentum. Of course, in a line that expresses a sense of, you know, doubt, this is actually pretty appropriate. In this line, the speaker is not confident (like the miser) that he'll be able to safeguard his treasure. That lack of confidence, subtly, is also communicated in the very minor hitch in Shakespeare's meter here. In that way, the rhythm underscores the content.
So there you have it. Of course, to really get a sense of the full range of Shakespeare's rhythmical effects, try reading the poem to yourself a few times out loud (you could even try to memorize it). You'll probably find bits of cool language rhythms coming back into your thoughts when you least expect it. And this is a great trick for parties. All your friends will just think you're the coolest Shakespearean on the block.