How does uppercasing work in poems in English? [closed]

I'm not a native English speaker and my education on English poetry is non-existent. I recently run into Shakespeare Sonnet 116 (reading the book The Elements of Eloquence) and I'm confused by the use of uppercase letters. The whole sonnet goes like this:

Let me not to the marriage of true minds
Admit impediments. Love is not love
Which alters when it alteration finds,
Or bends with the remover to remove:
O no; it is an ever-fixed mark,
That looks on tempests, and is never shaken;
It is the star to every wandering bark,
Whose worth's unknown, although his height be taken.
Love's not Time's fool, though rosy lips and cheeks
Within his bending sickle's compass come;
Love alters not with his brief hours and weeks,
But bears it out even to the edge of doom.
   If this be error and upon me proved,
   I never writ, nor no man ever loved. 

and just on the second line you can see an uppercase letter that is neither a proper noun, nor the beginning of a sentence. How does this work? is the uppercase telling me anything? Is it arbitrary? Should I only use the periods to know when a sentence starts/ends?

I was reading this poem out loud without having read it before and I had trouble knowing when sentences start and end.

The pattern in this sonnet seems to be that every line starts with an uppercase later regardless of whether it's the beginning of a sentence or not, but I don't want to infer anything from it.

Solution 1:

Poetry is art, it doesn't always follow the rules of punctuation or grammar. Normal capitalisation may apply as a rule of thumb, but don't be surprised if you see some writers ignore this. It can be an artistic choice.

Many poems use capital letters for the first word in every new line. However, what constitutes a "new line" depends on your point of view. In prose, a "line" may refer to a whole sentence, but in poetry, a sentence may span several "lines", depending on the structure of the poem which can take many, many different forms.

Here's a short "poem" as an example:

This is a poem.
It's not very strong.
I'm just proving a point,
that's why it's not long.

I have chosen to capitalise the second line of the poem because it is also the start of a new sentence. I have shown this by using normal punctuation. I haven't capitalised the final line, because it is a continuation of the third sentence in the poem - it just appears as a new line because of the structure and the rhyme scheme. In other words, I've used the normal rules of punctuation and capitalisation that apply to prose.

In your example, each new line is capitalised despite the punctuation - that may be characteristic of the period (as is evident by my poem, I'm no poetry expert) or it may have just been an artistic choice.

Haikus are considered a form of poetry, and they do not usually use capitals for each new line - for example, these two haikus from Matsuo Basho (1644-1694), considered the greatest haiku poet:

Autumn moonlight-
a worm digs silently
into the chestnut.

In the twilight rain
these brilliant-hued hibiscus -
A lovely sunset.