that's why in formal essays?

Question

"I'm", "it's" are forbidden in formal essays. Can I use "that's why" in the opening of my Statement of Purpose? > Fancy flights used to fill me with euphoria, that's why I named myself Joseph, but now ... It sounds a little awkward to use "that is why," though I'm not a native English speaker.

Answer 1

In this sentence, please note you have two coma splices where you need a period. That's why I named myself Joseph is a complete thought. Formal writing, such as a research paper, should use formal English. The contraction is seen as too informal. In the narrative essay, where the author is speaking in his/her own voice, and therefore mimics the rhythms of speech, contractions are acceptable.