Paul routinely had very valuable work in his collections, but he did not collect for money. He was a purist-collecting for the sake of it. He would expend endless energy in amassing collections, and when he decided to move on to something else, the collection would be sold outright, or handed off to a dealer, given away, and, I'm told, that occasionally art ended up literally on the street.

Paul did a famous Art Nouveau show at Finch college; another on American Realism. He collected American drawings and watercolors, setting standards and tastes for art through his selections. Many of his shows traveled widely. In fact, one of his key "marketing" techniques for his collections was to place paintings both in shows and as loans in small museums around the country, and then use those shows to add value to the collection.

When asked by Cumming about collectors, Paul had definitive opinions:

No one can define the word collector. That's a very loose term which has nothing to do with anybody today. The only real collector I've ever known or heard about in my lifetime was J. P. Morgan. He was a collector. The Wrightsmans are not collectors. They're agglomerators and they accumulate certain gold boxes and a few pieces of French furniture. Linsky is a collector, he buys lovely things. But the term 'collector' is a very loose one. I don't think Ben Heller is a collector. I mean he accumulated a certain number of pictures. But J. P. Morgan was a serious collector. I think Andrew Mellon was a collector, a mint collector, not because he put money into things but he collected vast, vast things. Kress was a collector from the word go, from the minute he could breathe he was collecting and buying. And of course the Europeans had a great tradition of collecting... I suppose Paul Sachs was a collector, too, but with a view in mind. And Lessing Rosenwald, of course, is a supreme example of a distinguished American collector. Perhaps after Kress, Widener and Mellon the collector in America.

A collection was more than a group of amassed expensive objects, Paul said. It had to have depth, it had to have intent, and it had to be informed with the knowledge of the collector.