Undergraduate students were presented with word pairs (e.g., egg-yolk) and were timed as they decided whether one word named part of the thing named by the other word. In Experiment 1, "no" responses to nonpart pairs (e.g., fish-flaps) were slowed by the similarity of the stimulus part (flaps) to a part that the stimulus object did possess (fins). This suggested that decisions were made by retrieving parts of the stimulus object from memory and comparing them to the stimulus part. Whereas the parts used as stimuli in Experiment 1 were nonspecific, belonging to several different types of object (e.g., wheel), those selected for Experiment 2 were specific to a single type of object (e.g., thumb). In Experiment 2, "no" responses to nonpart pairs (e.g., foot-thumb) were slowed by similarity of the stimulus object (foot) to an object that the stimulus part (thumb) belonged to (hand). This suggested that decisions were made by retrieving the object to which the stimulus part belonged and comparing it to the stimulus object. The results support a hybrid model of part-whole decisions that includes directed retrieval of relational knowledge from memory and a comparison process.