This paper probes into implicit language aptitude (LA), a set of cognitive abilities that showcase learners' unconscious, automatic second language (L2) attainment. Implicit LA is becoming an important part of aptitude research, and advances the understanding of L2 learning mechanism. This paper critiques the construct of implicit LA and proposes that implicit learning ability and implicit memory ability are two key components of implicit LA. We then explore the measurements of implicit LA. We raise a number of caveats derived from the validation of these measurements, and discuss how to circumvent these issues. One apparent reason for these caveats is the lack of empirical research that focuses exclusively on implicit LA, and thus, aptitude researchers are encouraged not only to include implicit LA measurements in their test batteries, but also to address the connection between the construct and its measurements.