Apples and Reality

One thing that someone said when discussing the difficult topic of whether or not there are real apples was "How did the concept of the apple get into the mind?" If the apple did not really exist independent of our conception, there would be no plausible explaination for how we have the concept of the apple. This is what Metaphysical Realists would say. I would have to say that I agree. This is why I cannot figure out what is so bad about Metaphysical realism according to von Glasersfeld. He feels that you cannot logically talk about anything outsoide of your expieriences. I agree with this but, saying that there is in fact a real apple sitting on my desk is not, at least to me, talking outside of my expieriences. I guess what my rambling is tryin to achieve is getting the message across that I feel that the reason we have the concepts of things is because things must exist outside of our reality.