Dutch artists were strikingly less concerned about artistic theory than those of many nations, and less given to discussing their art; it appears that there was also much less interest in artistic theory in general intellectual circles and among the wider public than was by then common in Italy. As nearly all commissions and sales were private, and between bourgeois individuals whose accounts have not been preserved, these are also less well documented than elsewhere. But Dutch art was a source of national pride, and the major biographers are crucial sources of information. These are Karel van Mander (Het Schilderboeck, 1604), who essentially covers the previous century, and Arnold Houbraken ("De groote schouburgh der Nederlantsche konstschilders en schilderessen" – "The Great Theatre of Dutch Painters", 1718–21). Both followed, and indeed exceeded, Vasari in including a great number of short lives of artists – over 500 in Houbraken's case – and both are considered generally accurate on factual matters.