Overview
I cannot say that I am a grammar expert. Despite having engaged in a significant amount of professional writing, I still find that I get papers returned pointed out new grammar mistakes that I was unaware of. Additionally, what is considered good grammar is changing. For instance, you may have noticed I ended the previous sentence with a preposition. If you ever watched the movie With Honors, you know this is a no-no and would never be allowed at Harvard. However, today this is becoming more acceptable in certain instances where the wording is awkward and cumbersome to avoid ending with a preposition. I still generally try to follow this rule, but not exclusively.
This section just provides some simple guidelines and links to resources on common grammar errors that I see when grading papers and reviewing papers for journals. For some of these issues, such as when to use "while" and "although" that is being debated in the grammar world. As I am not a grammar expect, in these instances, I go with what I have seen in how APA style prefers or what I have learned is preferred in many journals using APA style. I should add that many of these I learned because they were my common mistakes at one time!
That versus Which | Although versus While | Affect versus Effect
Contractions and Apostraphes
This one is not only difficult to understand, but also is difficult to explain. Essentially, "that" is used in in when followed by a restrictive clause, or when the information following "that" narrows or becomes more specific with the content. In other instances, especially when what follows is a side comment, then you use "which." At times, it may be up to the author to determine whether they want what follows "that" or "which" to be restrictive of just a comment.
It is important, however, to be aware of the punctuation implications. With "which," you use a comma before; however, with "that" no comma is needed. If you are still confused, I'd suggest the two links below which are probably clearer explanations than mine!
Kent College of Law Guide on That versus Which
Grammar Girl - with Pod Cast
This one is a little easier, but a common mistake. On many of my writing projects I will still search the document for every instance of "while" to see if I used it correctly. In general, most of the time when you are confused about whether "although" or "while" is correct, it is likely that you should go with "although." "While" is used when to mean "at the same time." "Although" is used in most other instances and is strongly preferred when using a comparison.
As the Grammar Girl link below notes, there are different interpretations on this. However, I have found that that most APA editors are clear in preferring the more reserved usage of "while" to cases meaning "at the same time."
This one took me a while to learn how to use correctly; my mind was just stubborn on this one. Even though the distinction comes pretty naturally to me now, I still find that I am not able to explain it very well. So let me just point to some links that do a better job than I could.
Owl Lab on Affect versus Effect
This one is pretty simple. In informal writing, go ahead and use contractions as much as you'd like. However, in scholarly writing, you would do best to put the contractions away. Notice the contrast in the two previous sentences: "you'd" versus "you would." You may notice that the contraction sounds more like slang or informal. That is the way it is perceived. You will sound more scholarly and professional if you avoid the contractions in your writing. So get rid of "can't" "won't" "didn't" "I'll" and all their friends when writing for a professional audience. But feel free to pull out these old friends when writing a letter or Email to a friend.