To respond to a positive statement, you can be lazy and just say 'Me too'. Or you can practise your grammar and use a 'so' response, by echoing the auxiliary or modal verb. I can say this --------- So can I I'm saying this -------- So am I I'd say this --------- So would I I've said this -------- So have I and so on. If it's a simple tense, without an auxiliary or modal verb, you use 'do' or 'did'. I say this every day - So do I. I said this every day - So did I. The same goes for negative statements. You can be lazy and respond to a negative statement with the all-purpose 'Me neither', or you can practise your grammar and make echo responses with 'Neither do I' , 'Neither can I, 'Neither will I' and so on.