Set of 4s against river aggression

[keikiwai]

The question is whether you think he's bluffing or not.

If he's bluffin you should call.

If you think he plays Q9, 96, or Q6 like this you push.

If you think he was slowrolling the flopped straight, you should call, because you can't be sure enough.

It's call or push here. I don't think you can be 60% sure, or whatever it is, that you're beat, so folding is not an option.