[cat_with_no_eyes]

I'm finishing my science essay and the body of the essay is in third person, but can the introduction i.e. opening paragraph and ending conclusion be in 1st and 2nd or do they have to be in 3rd person?

[imatfaal]

No - unless it has been specifically requested. 

for every case of "I think that..." replace with "So-and-so, in this-work, argues that ..."  It's a terrible thing, but your opinion isnt important; every argument must be backed up with either evidence or a reference to an old fart who has published.  Writing in the second person is weird in anything but fiction - and frankly it's a little disconcerting even in fiction.  If you really think you need to use the first/second person- eg "You or I might think this but research has shown otherwise" then find a way of using a third person stand-by.  Law uses the "reasonable man" or "the man on the clapham omnibus", others use "the man in the street" or the average person.  Many academics, quite unreasonably, take against any essay using first person pronouns.

By the way, and don't tell anyone I said this, google scholar and google books can be a really good way of finding an impressive looking quote/reference for something.  Put your idea into the search box and google's very clever machines bring back established authors who have said similar things - reference mining made easy.

Matthew

[PhysBang]

If you use a quotation, do not forget to introduce the quotation and explain the meaning of the quotation.

[JP]

You can, but you probably shouldn't.  If you're experienced with writing essays and you know exactly why you want to break the rule of writing in 3rd person (if there's something you want to convey that requires breaking that rule) you can do so.  But generally it's safest to stick to 3rd person throughout.

[Bored chemist]

Are we talking about first person vs third person or active voice vs passive voice here?

[Variola]

Are you being asked to  reference your essay? I ask because it is important to how you word your essay, if you haven't been asked to fully reference it then don't worry. But if you have then it is vital you reference quotes you have written to get round the 3rd person thing.

[josephmark98]

- I have subscribed this thread for further referance.
Regards