Here are some specific suggestions... 1. He used to be prone to anger. -- He was prone to anger in the past. (used to be prone sounds forced) 2. Humans tend to make mistakes when they are under high pressure. -- This sounds great. 3. He used to tend to become angry whenver someone gave comment on his dressing. -- He used to become angry whenever someone commented on his appearance. (tend to is not needed and seems awkward) (Using dressing here sounds like someone is commenting on salad dressing but I believe you are referring to clothing.) -- He tended to become angry... (this can be done but again sounds forced.) 4. I am inclined to mess them up when I do things in a hurry. (Here can "tend to" be the substitute of "be inclined to"?) -- I am inclined to mess things up when I do them in a hurry. -- I tend to mess things up when I do them in a hurry. (Both are correct, yet the second with 'tend to' sounds more natural. Use the object and then the pronoun that addresses it in this type of sentence. I would switch the words things and them like I have done in these examples.) I hope this helps. Mat