Testimony is Evidence

[SteveII]

The phrase "when relying solely on witness testimony" is a key component to 3' and cannot be left out in your reformulation without substantially changing the meaning.

It is certainly no circular. It's probably the fact that it is so obvious that makes it seem that way. 

"Care" (from 3') would include assessing background information that helps us determine if we can rely on it: the witness's character, cognitive ability, subject knowledge, experiences, and track record as well as the context of the event. If these things do not increase the likelihood of truth, then by all means reject the testimony. The point is that the GB's 3 does not allow for this possibility at all.

Damn!  I really thought I had something there, haha!  😛  But, my failed take down doesn't change what I was saying before; that all of this is theoretical, and based on heavily subjective metrics.  Your conclusion basically says, "don't accept unreliable testimony."[1] What practical purpose does that serve?  How does that advance our ability to distinguish between good and bad testimony in any real world capacity?  How do you suppose we apply this?  By using more testimony?  [2]

 You say, "if these things do not increase the likelihood of truth," but you have no actual way of measuring or quantifying results.  You have no way to demonstrate that "being careful", what ever that means (all this "background info" is similarly subjective, and so it may mean something different to you than it means to me) is a MORE reliable method, or at least AS reliable a method to the truth of a claim as simply withholding belief until stronger evidence arises. [3] All you have is syllogism hanging in space.

1. Remember the context of my post. I was comparing 3 and 3' --illustrating that both follow from the same premises (evidence) and the conclusions were written to address the specific question of relying solely on witness testimony. This means that both are opinion. There is no warrant in the evidence to say one is correct. My opinion matches most the world's opinion. 

2. The evidence presented addresses this question. There are way to improve reliable outcomes: double-blind lineups, sequential lineups, jury instruction, ask for confidence statements, etc. 

3. Witness testimony is subjective by definition. Similarly, assessing a complete witness testimony is also subjective. Does not change the fact that it is necessary nor will it ever be perfect. 

You do acknowledge that we accept witness testimony (sometimes on it own) every minute of every day right? Because the way you go on an on about this implies that the idea is irrational, and by extension, every legal system in the world is irrational.