If you read enough poetry, one thing you may notice is that poetry doesn’t always follow grammar rules. Sometimes subjects and verbs don’t match, other times the wrong verb tense is used, and in other situations word order is incorrect. This brings up something worth looking at: should poetry follow proper grammar rules?
One argument in favor of using proper grammar in poetry is that it helps with understandability. If a poem is written using proper grammar, however obscure its meaning might be, at least a reader could read it and make sense of the words and basic ideas.
Another reason to use proper grammar is that it can help prevent what might be considered “poetry cheating”. Sometimes in writing poetry using incorrect grammar can help a poem fit to a form. Other times it might sound nice and provide an effect. This though might be considered an easy way out. Rather than writing something in a proper way, which might take some work, a poet can just use improper grammar, and get their message across. There is some argument that a poet would be better served to take the time and write something in a proper way, rather than taking the shortcut.
Another reason to use proper grammar is that it enhances language. Language changes over time. There is some thought though that improper language takes over proper language. Slang replaces standard words. Incorrect word usage becomes common. The use of improper language could be enhanced by poetry that applies it. It could spread use that does not conform to standard. Enough of this, over time, could aid in the deterioration of language. If proper language is used though, it could help encourage its use.
There are reasons to use improper grammar in poetry though.
First, poetry is poetry. In some sense there are no rules. There are no grammar authorities that will chastise a poet for using incorrect grammar (outside of possibly a classroom or editorial setting). A poet can write how they like. They can use language how they like. They don’t have to follow any rules. This is one of the benefits of poetry.
Second, as mentioned above, incorrect grammar can sometimes sound nice. Sometimes changing word order can have a dramatic effect. Sometimes incomplete sentences can have impact. Sometimes the wrong verb choice can actually enhance a poem. This is part of poetry. Sometimes writing with improper grammar can actually make a poem sound better and be more impactful.
Third, and somewhat the other side of the coin from an idea mentioned above, improper grammar in poetry can help language evolve. Maybe a poet comes up with a clever word usage or ordering, that while not correct, sounds good and catches on. What the poet did could catch on and might change how language is used. It might enhance language by changing it.
Using proper grammar in poetry is one of those things that each poet will have to think about as they write. Sometimes, a poet will naturally write with proper grammar. In other situations, writing properly will be a conscious effort. Other times, it might sound better to break the rules. A poet will have to decide whether or not they value proper grammar in their poetry and how much effort that want to apply to using it. They will have to decide in each poetry situation how important it is.