I was watching this video about Cyclopia on youtube and noticed this sentence: How does an animal that normally has two eyes develop just one in the center of its face.

I tried to google it but I couldn't find an answer, and it's really nagging me. So, shouldn't it be "develops" being the subject of the verb "an animal"? Btw, I also heard someone saying "It doesn't seem safe", instead of "It doesn't seems safe" in a movie. Can someone explain to me the proper usage, and if you can keep it simple, please... I'm not a native speaker, and most of my English I learned from watching movies and tv shows, I'm just now trying to learn about grammar and stuff.

Ps: Was this post to lengthy? That's my first time here on stackexchange and I'm not really sure how I should approach writing my questions.

  • "Develop" is the infinitive. "Does" is an auxiliary verb, so when it is conjugated, the main verb is not. Auxiliary verbs in English are not used with conjugated verbs, they are always used with some non-conjugated form like the infinitive or a participle.
    – sumelic
    Oct 16 '17 at 0:28
  • Just to make sure that I understood. The presence of an auxiliary verb means that the pronoun is being conjugated so there's no need to conjugate the verb? Btw, thank @sumelic for your feedback and I'll make sure to post my future questions if they are as simple as this one on the Learners stack. Oct 16 '17 at 0:37
  • The auxiliary verb is what is conjugated. For example, because "an animal" is third-person singular, we use the auxiliary "does", the third-person-singular conjugation of "to do". The word "develop" is not conjugated, because it is being used as an infinitive in a construction with the word "does".
    – sumelic
    Oct 16 '17 at 0:40
  • Yeah, I got it after reading the post your cited on ELL. Wow, this community is really dynamic. It's like Twitter, I didn't think it would be that easy to clear up my doubts about grammar. It's really cool to find a place on the web with so many language enthusiasts. Hmm, I probably shouldn't be blabbing in here about my random awe. Anyway, thank you for your help I probably wouldn't be able to sleep until I got this cleared up. Oct 16 '17 at 0:53

When you use an auxiliary verb for a third person, the main verb loses its 's.'

He walks toward a church
He does walk toward a church.

However, this change doesn't happen in first person; because, there is no 's' in the verb.

I walk toward a church
I do walk toward a church.

Especially when you are forming a question, the auxiliary verb is mandatory.

He walks toward a church? ~ Not a preferred structure as a question.
Does he walk toward a church? ~ Preferred structure

Why? Well, the questions are formed that way only.

It doesn't seem safe

You don't put 'seems' there because, as I said, when you put an auxiliary 'does' there, you remove 's' from the verb. Remember that way - the main verb's 's' is eaten by the auxiliary verb. But remember, this is not always a case.

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