Even though INTP and ISTP both have a Ti as their dominant function, there is quite a bit difference in their representation. INTP are known as people that have breath of the knowledge, while ISTP are known as specialist in one specific knowledge.
I don’t agree with that notion on any level but very superficial. I think that just like ISTP, INTP go deep into the subject matter. It is just that their auxiliary Ne sometimes makes them check more than one speciality.
This contrasts with that little subset of Te dominant or Te auxiliary that I have met so far. They are much more likely to have opinion on basically any subject that a person can bring up.
These difference come from the fundamental differences in how Ti and Te relate to the world.
Extraverted thinking is an extraverted judging function. What does this imply is that extraverted thinking is much more interested in what is going on in the outside world than the inside one. The introverted thinking is the reverse: much more interested in the inner world than the outside.
Other functions have this as well. Let us take sensing. Extraverted sensing is interesting in what is going in the inside world. The introverted sensing is much more interesting in the current feeling of the body and sense of self.
That leads us to the first difference, and that is how both of them are perceiving the subjective data, like personal impressions, experience and their own learning.
Extraverted thinking finds the subjective data to be there only to obscuring the real truth. On the other side, introverted thinking accepts subjective data as completely valid facts.
Which also brings us to the second difference, how they come to the acceptance of a fact.
Extraverted thinkers are much more likely to simply accept an assumption, assuming that they can be certain that it came from the credible source. So a pupil in primary school with the extraverted thinking is much more likely to simply accept that the Earth is round, because it says so in the textbook. They assume the facts are true, because they want to reach a conclusion as quickly and as efficiently as possible.
No that they will believe anything they hear.
Introverted thinkers are much more likely to question the facts. In the true perceiving fashion they are much slower to reach a conclusion. They painstaking make sure the data and facts are corrects beforehand. The good example of this is my diet. You can tell me that some diet, like eating only organic fruit and vegetables is good for me. But I tried it and I did not notice any difference. So for me this fact is not right. But I could only said that after I tested it for myself. And sometimes these tests can only be done in head, which is probably how the mental exercises, like the Schrodinger cat come in existence.
Also, knowing why something is true can be a valid shortcut for reaching the acceptance of the validity of the fact.
This upper fact does point to another difference. Introverted thinkers are people that are enjoying the journey and the journey itself is much more important than the end. They are the one that are more likely to take action.
The extroverted tinkers are different, as they want to reach the results, so called end, as soon as possible. The enjoyment of the journey is not as important to them. They are more likely to reach a results.
Which clearly shows, when you ask a person a question that is from from the area in which they are competent in. Introverted thinkers are going to start pondering and questioning the subject at hand. Extraverted thinkers are going to find some facts and reach a conclusion as soon as possible.
Let me return the the upper point, that I don’t think that INTPs are the breath types of thinkers. From the upper data, we can say that extraverted thinkers are more of the breath types of thinkers, while the introverted thinkers are more of a depth type of thinkers. So from this analogy, INTPs would be, like ISTPs, more of a specialists.