This document discusses sources of intralingual errors in second language acquisition. It defines intralingual errors as those that occur due to faulty or partial learning of the target language rules. Four main types of intralingual errors are discussed: over-generalization, ignorance of rule restrictions, incomplete application of rules, and false concepts hypothesized. Examples are provided for each type of error to illustrate how learners may incorrectly apply rules of the target language in their speech and writing. Tables listing common verb and preposition errors found in learner language are also referenced.