Always go with the grammatically correct keyword, Rebecca. Jay has touched on this more than once in his webinars.

Aside from the possibility of being penalized by Google as Marc had mentioned, you also want to keep in mind that your website is your brand, so to have keywords that are grammatically incorrect could reflect negatively on you and your brand.

Great responses from everyone. There is one more thing I would like to add. If you use the term "learn sew seeing machine" you could get penalized by Google. However, if you change it to be grammatically correct. "Learn to sew by seeing me sew on my machine" You would still be able to capture the incorrect grammar keyword as well. This is the LSI part of Google. So you could capture both longtail keywords without ever typing the incorrect one.
As your website grows you will find that you rank for things that you never actually wrote but are semantically the same.
I hope that helps.
Marc

Great comments below I learnt a little bit

This is a great question and one that seems to pop up from time time. What people search for and how they do it will always be subjective. Google doesn't care about bad grammar but your visitors will. Watch here: https://goo.gl/254SqB

Some also tend to ignore Google's suggestive spelling by asking: "did you mean ...?"

Typos can be a turn-off to visitors even if they make them themselves. Some suggestions are to include typos in the alt field for images or elsewhere but one has to be careful with these "techniques."
A safer suggestion maybe is to have a section such as "usually spelled like this or commonly referred to as..." somewhere in your article.

From my memory of the training here by Kyle and Jay, we are encouraged to correct our keyword results. We are the standard in spite of.

Hi Rubecca, I know that in many live trainings with Jay he stresses using keywords that make human sense as he puts it. At this point in my experience I am so focused on just creating content that although I use Jaaxy and love it. I don't allow myself to get bogged down with specifics. I have learned that the more content I write the more I learn about how to use all these tools. It's kind of a weird "Paint the Fence" effect.
Damo

Hi,
The short answer is that you will likely not be able to maximize search results using grammatically incorrect search terms.

When you see a phrase that is grammatically incorrect and fix it to make it correct, you are actually using a totally different keyword phrase that is going to have different results.

Some people try and use those grammatically incorrect phrases in their content, but its NOT a good idea to that, as it makes your content read shoddily, which in turn provides a bad user experience to your readers. Readers don't like to struggle through posts and pages with bad grammar that is hard to read, or doesn't make sense. Readers are likely to click out of such websites and go elsewhere for what they are looking for.

Like the training says, focus on grammatically correct phrases. Look for those longtail keyword phrases. They may not have a lot of searches per month, but if the competition is low you are sure to rank. You get a couple dozen posts with such keywords and you will be getting found easily, and people will be staying on your site to read your content because the grammar is descent.

Keywords can hard to grasp. Back when I was learning this stuff a couple years ago on my own I struggled.

Best of luck!
TD

The short answer is you don’t :) Only use the keywords that make grammatical sense. Sometimes it’s just a matter of tweaking the keyword to get a better traffic/competition ratio, but just like Kyle says, it’s very important to only use keywords that make grammatical sense.