[MikaMay]

I would like to add to gmacloed's post another important point-- generally speaking, it's not even a matter of a puppy *understanding* at such a tender age because puppies that young do not even have the *physical capability* to hold it very long because their bodies / bladder muscles are still undeveloped. So to expect a puppy to hold it is unrealistic.

The housetraining process is a combination of getting the idea in their little heads PLUS allowing their bodies to mature enough to be *able* to hold it. Puppies' bodies can't do this until or about 5 to 6 mos. of age (definitely over 4 mos). That is why so many people will tell you it takes until the pup is about that age before you'll see progress in their housetraining...