許多發展心理學家認為由於接觸到詞彙，就會使人們在陌生的概念間建立界線(例如：Bowerman and others (1996)、Gentner and Boroditsky (2001) 、Gopnik and Meltzoff (1987); Gopnik,Meltzoff and Bryant (1997) 、Waxman and Markow (1995) 、Waxman and Thompson (1998) )。
跟小孩子說這兩種不同的話語時，小孩子會有不同的反應：「See this one. Find another one.」和「See this fendle. Find another fendle.」(Markman & Hutchinson, 1984) ，前者小孩子會根據空間或可能一起出現的事物選擇，例如選擇一個骨頭搭配狗；後者則會選擇相同類別的事物，把一隻台灣土狗選擇另一隻博美狗搭配。詞語可以使人們建立一個類別。小孩本來就會知道台灣土狗和博美狗是同一個類別「狗」，狗這個概念是在聽到「fendle」前就存在的，而詞語的角色就是讓小孩子知道在這個脈絡下它們是一個類別。詞語的功能在於在使小孩子的目光放到一個心裡本來就存在的類別。
引用Bloom (2000)的說法：當小嬰兒耳朵發炎的時候，我們會放一個小管子到耳朵裡，讓耳朵裡的體液可以流出來，很俗地講就是「耳朵裡的管子」，但是這個東西有一個專門的名字「grommets」。我們學會「grommets」這個詞，並不表示我們產生了一個新的類別，我們只是不知道這個東西的名字而已。如果所有的詞語學習都是這樣的運作過程的話，那麼詞語並沒有幫助我們形成任何新的概念。
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