The ISTp I dated was at least capable of expressing his evaluations of a topic. If he felt I should know it, at least. Also, he would sometimes ask me why I felt a certain way about a topic, and actually LISTENED to me and sometimes responded in kind. If we disagreed about something, it didn't affect our relationship much.
The ISTj I dated would judge my actions/words, show it in his body stance and eyes, but would not (could not?) express it in words. He would not even listen to my explanations of why I chose such and such action. My explanations seemed to go in one ear and out the other. It's as if he'd make his judgement, and nothing in the world could penetrate through it. We lasted one stupid little disagreemeent, I was busy with a crying daughter so I couldn't immediately attempt to resolve it with him, he walked out of my world 2 minutes later. (Thankfully, as that was a very stressful relationship to maintain.)