I say
1. A phrase used for emphasis. I say, my good man, can you take my coat?
2. An phrase used to express surprise and/or incredulity I say, it feels like it's been raining every day for a month!
3. A phrase that precedes one's opinion or view. Since it’s already 10 o'clock, I say we just stay in for the evening.
I say
1. Used preceding an utterance to call attention to it: I say, do you have the time?
2. Used as an exclamation of surprise, delight, or dismay.