It agrees with theoretical predictions about how the variable being measured is related to other variables. It seems comprehensive and matches the conceptual definition of the variable. Improving one tends to improve the other. They are unrelated. Improving one tends to decrease the other.
Internal validity is a subset of external validity.
External validity is a subset of internal validity. Read the following scenario and answer the next four questions. An education researcher is interested in the effectiveness of a new method of teaching reading to 1st graders. She divides the students into two groups and gives each of them a reading test. She trains several teachers in how to teach reading using the new method.