The reason why the first person should be avoided, is that in scientific writing one’s opinions, feelings and views are not regarded as important. Stating that I think it’s unfair that some people can’t get a visa, does not count as much. However, urging you not to use I in essays can fail in two ways. Firstly, you could still write about your own feelings and opinions using different phrases, and secondly, not all uses of the first person are bad. It’s a good idea to stay clear of phrases such as “I think,” or “in my opinion,” unless you’re evaluating a claim. However, there is no apparent reason for not saying “I will first define the key terms.” Using the first person in this way will make a text more approachable. Moreover, using phrases starting with I, you avoid using the passive voice which many find more difficult to read.
Having said this, some markers still consider it preferable not to use the first person. Should your tutor or marker be one of them, you may want to play it safe. Don’t use we when you mean I. If you are the sole author, the use of a plural is technically not correct. However, even a tutor who hates such phrases will not mark you down: It’s the argument and general structure of your essay that count for much more.
One area where there is no room for argument is the use of colloquialisms, slang, or street language. Academic writing is formal writing, and you might be penalized for using the wrong register. A little bit of informality here or there will