Knowledge by acquaintance

In philosophy, a distinction is often made between two different kinds of knowledge: knowledge by acquaintance and knowledge by description.

In 1865, philosopher John Grote distinguished between what he described as "knowledge of acquaintance" and "knowledge-about". Grote noted that these distinctions were made in many languages. He cited Greek (γνωναι and ειδεναι), Latin (noscere and scire), German (kennen and wissen), and French (connaître and savoir) as examples.

Grote's "knowledge of acquaintance" is far better known today as "knowledge by acquaintance" following Russell's decision to change the preposition in a paper that he read to the Aristotelian Society on 6 March 1911.

In a similar fashion, in 1868 Hermann von Helmholtz clearly distinguished between das Kennen, the knowledge that consisted of "mere familiarity with phenomena", and das Wissen, "the knowledge of [phenomena] which can be communicated by speech". Stressing that the Kennen sort of knowledge could not "compete with" the Wissen sort of knowledge, Helmholtz argued that, despite the fact that it might be of "the highest possible degree of precision and certainty", the Kennen kind of knowledge can not be expressed in words, "even to ourselves".

In 1890, William James, agreeing there were two fundamental kinds of knowledge, and adopting Grote's terminology, further developed the distinctions made by Grote and Helmholtz:

According to Bertrand Russell (1905), knowledge by acquaintance is obtained through a direct causal (experience-based) interaction between a person and the object that person is perceiving. Sense-data from that object are the only things that people can ever become acquainted with; they can never truly KNOW the physical object itself. A person can also be acquainted with his own sense of self (cogito ergo sum) and his thoughts and ideas. However, other people could not become acquainted with another person's mind, for example. They have no way of directly interacting with it, since a mind is an internal object. They can only perceive that a mind could exist by observing that person's behaviour.

To be fully justified in believing a proposition to be true one must be acquainted, not only with the fact that supposedly makes the proposition true, but with the relation of correspondence that holds between the proposition and the fact. In other words, justified true belief can only occur if I know that a proposition (e.g. "Snow is white") is true in virtue of a fact (e.g. that the frequency of the light reflected off the snow causes the human eye, and by extension, the human mind, to perceive snow to be white). By way of example, John is justified in believing that he is in pain if he is directly and immediately acquainted with his pain. John is fully justified in his belief not if he merely makes an inference regarding his pain ("I must be in pain because my arm is bleeding"), but only if he feels it as an immediate sensation ("My arm hurts!"). This direct contact with the fact and the knowledge that this fact makes a proposition true is what is meant by knowledge by acquaintance.

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