It is generally agreed that sympathy is an exchange of feelings between two parties, one who suffers and one who observes and reacts to the suffering. The names given to these parties are more various and indistinct in meaning than those assigned to the feelings themselves. They come under the following headings: self, consciousness, individual, person, character, object, identity, substance, thinking thing and soul. The most usual term is person, and it is the one chosen almost exclusively by Smith, as in his celebrated summary of the work of sympathy given at the outset of The Theory of Moral Sentiments when he supposes a scene of torture and asks what our senses combined with our imagination are capable of performing while watching it. His answer is as follows:

Here then is a limited transaction between two individuals called persons, each bounded by a history of sensations which are their very own, not to be shared other than by means of an imagined case or hypothesis, a fiction (an imagined description or narrative) of what the sympathizer's own sensations would be in such a situation.

Among the thinkers we have discussed we can see that many would agree with this principle of an unbreachable core of personhood, including Descartes, Shaftesbury, Hutcheson, and Hazlitt; for they would argue that sympathy is unlikely to succeed if the person suffering is overwhelmed by passions, unseasonably moved and indistinct, or if the person sympathizing is so far invested in the passions on show as to lose the sense of agency.