"THEN" and "THAN"

"Then" relates to time. "Than" is used for comparison. Ex.: First, we'll have lunch, and then we'll go for a walk. He is more experienced than I am.

"IMPLY" and "INFER"

"Imply" means to suggest indirectly. "Infer" means to deduce or conclude from evidence. Ex.: Her silence seemed to imply disapproval. From her reaction, we can infer that she is unhappy.