Consider two lives. Helen Keller was born blind and deaf, but her access to the written word enabled her to succeed as a writer and activist.

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Question: What is your summary of the author’s main ideas. Post your own answer in the comments before reading those made by others.

Consider two lives. Helen Keller was born blind and deaf, but her access to the written word enabled her to succeed as a writer and activist. Peter the Wild Boy, discovered near Hanover, Germany in 1719, possessed sight and hearing, but was innocent of language. He left the world as innocent as he came. “Without artifice, particularly the shared human artifice of speech, an unmeaning silence traps Peter in an unvarying bestiality”.

The stark comparison illustrates the degree of our dependence on the word of others. Without the ability to give and receive testimony, we cannot transcend the limitations of our individual faculties to borrow from the thoughts, observations, and experiences of others. The kind of knowledge that separates human beings from the rest of the animal world disappears. While a deficiency in one’s sensory faculties can perhaps be compensated for, inability to draw from the knowledge of others forecloses all possibility of higher knowledge.

The contemporary philosophical literature on testimony can be viewed as an elaborate set of footnotes to the debate between the great rivals of the Scottish Enlightenment: David Hume and Thomas Reid. The positions of Hume and Reid are not exhaustive, but the rift between them represents the continental divide in the intellectual landscape. The main point of dispute between them is whether testimony is a derivative source of knowledge (the “reductive theory”), or an irreducible, basic source of knowledge (the so-called “non-reductive theory”).

To the outsider this debate might seem pedantic. Even most academic philosophers spend relatively little time on it. So what is the big deal? At stake is whether we should accept a vision of human knowledge that prioritizes autonomy, avoidance of gullibility, and skepticism of external authority, or one that prioritizes trust and acknowledges our inescapable dependence on authority.

For Hume, we are justified in accepting testimony only to the extent that we have independent reasons for thinking the speaker is telling the truth. We must have prior knowledge that the speaker is honest, or recognition that what is said coheres with other things we know. To believe testimony that has not been so accredited is to be guilty of the sin of gullibility.

Reid, by contrast, claims there is a standing entitlement to accept testimony, though the entitlement can be nullified by sufficient counter-evidence. This “Principle of Credulity” results in a more egalitarian relationship between testimony and the senses. Being told by a fellow student that Professor Smith has just entered his office and seeing him enter his office are both sufficient reasons for believing that he is there, though they are not necessarily of equal weight.

In claiming that testimony is a basic source of justification for the hearer, Reid isn’t denying that testimony can work only in conjunction with other sources of knowledge. Just as memory extends pre-existent knowledge across time, testimony transfers pre-existent knowledge from one person to another. Testimony, unlike other sources of knowledge, is irreducibly social and morally significant. It cannot operate without trust on the part of the hearer and honesty on the part of the speaker.

In the contest between these two views, the reductive theory (Hume’s view) enjoys the advantage of simplicity. It postulates one fewer basic sources of knowledge. Theoretically, we don’t want to add sources of knowledge willy-nilly—each one must be explanatory or we’ll end up postulating psychic powers and the like. So the friend of the non-reductive theory is under pressure to explain how the additional basic source earns its keep.

C.A.J. Coady, whose work on testimony played a major role in reviving interest in the topic, claims the non-reductive theory of testimony is essential to avoiding skepticism. Few, if any, have witnessed the complete path of one letter, yet everyone knows how the postal service works. “Similarly,” Coady writes, “that babies are born of women in a certain way, is known to all of us and it is a fact of observation, but very many of us have not observed even one birth for ourselves”.

We flatter ourselves by thinking knowledge comes by our own devices, and not though implicit reliance on the vast, un-vetted pool of collective experience we take on trust. Ronald Reagan said, “Trust, but verify.” The Gipper would probably concede Coady’s point, though, that we place our trust in far more things than we can possibly verify “off of our own bats.” Given our extensive dependence on trust, attempting that would lead us to skepticism about ordinary things. Positing testimony as a basic source of knowledge is justified because it is necessary to help us avoid this unhappy result.

In theory, defenders of the reductive theory could simply “bite the bullet” and embrace skepticism. In practice, that never happens. Philosophers hate to admit that they don’t know things. So instead, they retort that testimony can deliver the goods as a non-basic source of knowledge. Rational acceptance testimony doesn’t require vast amounts of fieldwork, only the recognition that human beings normally tell the truth—something that individual experience can establish.

Armed with that knowledge, we can infer that particular pieces of testimony are likely to be true without positing testimony as a basic source of knowledge. Variations of this line of response have been convincingly developed by Paul Faulkner, Elizabeth Fricker, and David Lyons among others.

Such replies serve to blunt the main offensive of the non-reductive theory, but at a cost. Once friends of the reductive theory endorse a norm of accepting what we are told, they are in less of a position to distance themselves from their rivals’ theory on the grounds that it sanctions gullibility. Neutralizing the observation argument does not win the game, it only resets the board. The reductive theorist plays white; his one-tempo starting advantage is the appeal to simplicity. Given the strength of both sides’ arguments, the game will probably continue for some time.

Adapted from 1000 Word Philosophy.


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  1. Hume (reductive, must explain everything) vs Reid (non-reductive, must accept everything as truth), testimony = knowledge


  2. MIP: in order to obtain higher knowledge, we are dependant on others knowledge to build upon. hume and reid debate on testimony


  3. Testimony = reductive or non-reductive (Hume and Reid)


  4. Two schools of thought regarding a Testimony (Hume, reductive theory –> verify credibility of speaker) and Reid ( non- reductive –> must accept testimony as standing). Both have advantages and disadvantages.


  5. We are dependent on others for knowledge. 2 fields of thought = 1) reductive (believe only if you know it’s true), 2) nonreductive (believe if you can’t verify)


  6. MIP: testimony = source of knowledge + 2 diff opinions (Hume + Reid)


  7. There are two opposing philosophies on the topic of testimony: Hume’s reductive theory (claims have little weight without established trust or credibility) and Reid’s non-reductive theory (claims are usually trustworthy unless belied by contradictory evidence). Despite each side’s overarching claims, reality is a lot more situational and specific situations grant truth to one philosophy or the other.


  8. Goal: To compare two theories that contest whether testimony, the passing of information, is derivative or basic- the reductive and non-reductive theory (Hume & Reid)
    + of reductive: simplicity, not source of knowledge (we are skeptical)
    + of non-reductive: has support in contention humans usually honest. Proponent = Coady


  9. There is a big divide on the philosophy of testimony.
    Reductive theory, created by David Hume, says to only accept testimonies if you have individual reason to, such as knowing a person to be honest.
    Non-reductive theory, created by Thomas Reid, says to accept all testimonies because humans are likely to tell the truth.

    These seem to be more extreme philosophies if implemented to everyday life. Reality seems to be a mixture of both, but the divide between philosophers will continue. Tone = bringing knowledge to a philosophic divide.


  10. MIP: Hume’s reductionist approach = trust , Reid’s non-reductionist approach = simplicity


  11. main idea hume reductionist approach trust in the testimony, reid is simplicity.


  12. Reductive theory is a theory of communication that presumes that the information we are given through speech is true. Much of our knowledge of the world comes from communication, which makes this idea so important.


  13. There is a debate between the reductive (Hume) and non reductive (Reid) sources of knowledge. Author thinks both are strong but seems to favor non reductive.


  14. Research debates on the question whether testimony is a derivative or irreducible source of knowledge. Both are reasonable, and no definite answer yet.


  15. Two main thoughts on the acceptance of testimony – Hume (Reductive) and Reid (Non-reductive), both schools of thought will endure.


  16. Two different views on testimony – Hume (Reductive) – testimony = secondary source of knowledge and Reid (non-reductive) – testimony = basic source of knowledge. The debate will go on.


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