Alas, such an agreement is meaningless. We cannot (yet) measure sadness, quantify it, crystallize it, access it in any way from outside. We are totally and absolutely reliant on your introspection and my introspection. There is no way anyone can prove that my "sadness" is even remotely similar to your sadness. I may be feeling or experiencing something that you might find hilarious and not sad at all. Still, I call it "sadness" and I empathize with you.
This would not have been that grave if empathy hadn't been cornerstone of morality.
The Encyclopaedia Britannica, 1999 Edition:
"Empathy and other forms of social awareness are important in development of a moral sense. Morality embraces a person's beliefs about appropriateness or goodness of what he does, thinks, or feels... Childhood is ... time at which moral standards begin to develop in a process that often extends well into adulthood. The American psychologist Lawrence Kohlberg hypothesized that people's development of moral standards passes through stages that can be grouped into three moral levels...
At third level, that of postconventional moral reasoning, adult bases his moral standards on principles that he himself has evaluated and that he accepts as inherently valid, regardless of society's opinion. He is aware of arbitrary, subjective nature of social standards and rules, which he regards as relative rather than absolute in authority.
Thus bases for justifying moral standards pass from avoidance of punishment to avoidance of adult disapproval and rejection to avoidance of internal guilt and self-recrimination. The person's moral reasoning also moves toward increasingly greater social scope (i.e., including more people and institutions) and greater abstraction (i.e., from reasoning about physical events such as pain or pleasure to reasoning about values, rights, and implicit contracts)."
But, if moral reasoning is based on introspection and empathy - it is, indeed, dangerously relative and not objective in any known sense of word. Empathy is a unique agreement on emotional and experiential content of two or more introspective processes in two or more subjective. Such an agreement can never have any meaning, even as far as parties to it are concerned. They can never be sure that they are discussing same emotions or experiences. There is no way to compare, measure, observe, falsify or verify (prove) that "same" emotion is experienced identically by parties to empathy agreement. Empathy is meaningless and introspection involves a private language despite what Wittgenstein had to say. Morality is thus reduced to a set of meaningless private languages.
The Encyclopaedia Britannica:
"... Others have argued that because even rather young children are capable of showing empathy with pain of others, inhibition of aggressive behaviour arises from this moral affect rather than from mere anticipation of punishment. Some scientists have found that children differ in their individual capacity for empathy, and, therefore, some children are more sensitive to moral prohibitions than others.
Young children's growing awareness of their own emotional states, characteristics, and abilities leads to empathy--i.e., ability to appreciate feelings and perspectives of others. Empathy and other forms of social awareness are in turn important in development of a moral sense... Another important aspect of children's emotional development is formation of their self-concept, or identity--i.e., their sense of who they are and what their relation to other people is.
According to Lipps's concept of empathy, a person appreciates another person's reaction by a projection of self into other. In his Ästhetik, 2 vol. (1903-06; 'Aesthetics'), he made all appreciation of art dependent upon a similar self-projection into object."
This may well be key. Empathy has little to do with other person (the empathee). It is simply result of conditioning and socialization. In other words, when we hurt someone - we don't experience his pain. We experience OUR pain. Hurting somebody - hurts US. The reaction of pain is provoked in US by OUR own actions. We have been taught a learned response of feeling pain when we inflict it upon another. But we have also been taught to feel responsible for our fellow beings (guilt). So, we experience pain whenever another person claims to experience it as well. We feel guilty.
To use example of pain, we experience it in tandem with another person because we feel guilty or somehow responsible for his condition. A learned reaction is activated and we experience (our kind of) pain as well. We communicate it to other person and an agreement of empathy is struck between us.
We attribute feelings, sensations and experiences to object of our actions. It is psychological defence mechanism of projection. Unable to conceive of inflicting pain upon ourselves - we displace source. It is other's pain that we are feeling, we keep telling ourselves, not our own.
The Encyclopaedia Britannica:
"Perhaps most important aspect of children's emotional development is a growing awareness of their own emotional states and ability to discern and interpret emotions of others. The last half of second year is a time when children start becoming aware of their own emotional states, characteristics, abilities, and potential for action; this phenomenon is called self-awareness... (coupled with strong narcissistic behaviours and traits - SV)...
This growing awareness of and ability to recall one's own emotional states leads to empathy, or ability to appreciate feelings and perceptions of others. Young children's dawning awareness of their own potential for action inspires them to try to direct (or otherwise affect) behaviour of others...
...With age, children acquire ability to understand perspective, or point of view, of other people, a development that is closely linked with empathic sharing of others' emotions...
One major factor underlying these changes is child's increasing cognitive sophistication. For example, in order to feel emotion of guilt, a child must appreciate fact that he could have inhibited a particular action of his that violated a moral standard. The awareness that one can impose a restraint on one's own behaviour requires a certain level of cognitive maturation, and, therefore, emotion of guilt cannot appear until that competence is attained."
That empathy is a REACTION to external stimuli that is fully contained within empathor and then projected onto empathee - is clearly demonstrated by "inborn empathy". It is ability to exhibit empathy and altruistic behaviour in response to facial expressions. Newborns react this way to their mother's facial expression of sadness or distress.