椅子和時鐘都是人造物。豆子椅、搖椅、藤椅…等，都是椅子；數位鐘、可樂鐘、吊鐘，都是時鐘。他們形狀差異如此之大，如何形成概念？
有人認為這個概念有一個傾向功能(intended function)。這個東西可以用來做什麼？我們會知道某些東西是椅子、是時鐘。即使這個椅子壞了，一坐就倒；即使這個時鐘不再走動無法報時，我們還是會叫他們椅子、時鐘。
另外有一些人則認為被歸在同一類的人造物是根植於我們對於創造這個東西的人的傾向，以及如何將它和物體的設計進行關連(Dennett, 1990; Keil, 1992; Bloom, 1996; Bloom, 1998; 相關討論亦可見Malt & Johnson, 1998)。我們判斷某個東西是椅子，不是因此它和我們過去接觸過的椅在外形或功能上相似；我們之所認為這是椅子，是因為它的外形和功能和過去我們認為是椅子的東西有相同的傾向。
從本質論(naive essentialism或psychological essentialism)來看，或許人們不認為人造物如同自然物一樣存在潛藏的特質。但這並不否定屬於同一個概念的人造物在更深層的地方存在有共同的特質。人造物可能不像生物或化學那樣，它的本質是來自於社會和心理的(Putnam, 1975; Keil, 1992)。
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