This is a really confusing one. Sometimes Spock seems very ISTJ-ish because of his dogmatism and high principles, but also an INTJ-type, because he's also looked upon as a logical mystic.
He has the tendency to take things literally, which is not really an S or N trait, but more of an Introverted irrational function. I speculate that Si has a better understanding of what people mean because they have Ne as a fourth function, which possibly manifests itself in a practical understanding.
INTJ, on the other hand, is manifested quite differently. A dominant Ni is extremely self-absorbed and the least aware of its practical surroundings, and the inferior Se notices details, but without Ni instead of Ne, interpretations of the world are more about what you think something means rather than what it actually means.
What are your thoughts?