Four experiments examined the role of a pragmatic constraint, the modifiabi
lity of noun phrases (NPs), in the modification of complex NPs. Experiment
1 demonstrated that NPs that had received relatively specific prior modific
ation were less likely to take additional modification than NPs with less s
pecific modification. This effect was obtained in both Spanish and English
using 2 off-line tasks. Experiments 2 and 3 demonstrated on-line modifiabil
ity effects for both languages using a self-paced reading task. The results
further suggest that although Spanish and English speakers may have opposi
ng modification preferences, modifiability constrained their interpretation
s in the same direction. The results of Experiment 4 suggest that discrepan
cies between the off-line results from Experiment 1 and the on-line results
from Experiment 3 may be due to task differences. Implications are discuss
ed in relation to current models of sentence processing.