This particular post is in response to something that I see/hear often. Every now and then, I will hear someone make the claim "I know, in my heart, that it is true," or "We all know in our heart the truth." Usually, it is in a religious/emotional context. Someone will receive a peculiar emotional experience and become "high" off of the episode. They then feel the need to say that they know the truth because their heart acts in such a way! What tomfoolery!
The inaccuracy of such proclamations comes from the fact that the heart does no thinking; there is such a thing as modern psychology, as much as someone wishes to deny or ignore it. Our heart serves for purely physiological needs and does no more.
On the other hand, the brain does the thinking (or at least an engaging one does). Here, one might say that they know such a thing. To say "I know something in my heart" could be an alternative way of saying "I know something based off my feelings." Feelings are not a prerequisite of truth.