I'd like to understand the usage of 'either' and 'too.' Question 1 My textbook says 'either' cannot be used at the end of a positive sentence and 'too' cannot be used at the end of a negative sentence, i.e. s12 and s21 are correct and s11 and s22 are incorrect. Is that right? s11: Bob is tall, either. s12: Bob is tall, too. s21: Bob is not tall, either. s22: Bob is not tall, too. Question 2 But my textbook doesn't say anything about why. Oxford Pocket English Dictionary says 'too' means 'in addition.' If 'too' does mean 'in addition,' I think s22 should be correct too. The American Heritage Dictionary of the English Language says 'either' means 'likewise.' If 'either' does mean 'likewise,' I think s11 should be correct too. I understand why s12 is correct. s12 is correct because, I think, 'too' in s12 means 'in addition.' What does 'either' in s11 mean? Or why is s11 incorrect? Question 3 What does 'too' in s22 mean? Or why is s22 incorrect? Thank you.