Is the Star Test for Syllogisms a Valid Method?

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Discussion Overview

The discussion revolves around the validity of the 'star test' for syllogisms as introduced by Harry J. Gensler. Participants explore the implications of the test in determining valid conclusions from given premises, specifically examining examples and counterexamples related to syllogistic reasoning.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions the validity of the conclusion 'some B is C' from the premises 'all A is B' and 'all A is C', suggesting it may be valid despite the star test indicating otherwise.
  • Another participant points out a potential fallacy related to the Undistributed Middle Term, questioning the accuracy of the premises as stated.
  • A participant explains the mechanics of the star test, noting that the test requires each capital letter to be starred exactly once and that there should be exactly one starred letter in the conclusion.
  • One participant speculates that the lack of a necessary existence of A could explain the invalidity of the conclusion.
  • Another participant provides a concrete example using 'Ford', 'vehicle', and '4 wheels', suggesting that the conclusion could be valid in this context.
  • A different example involving 'fairies', 'things that have wings', and 'things that have magic wands' is presented, highlighting that the existence of A affects the validity of the conclusion.
  • One participant acknowledges a realization that the emptiness of A is a critical factor in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the validity of conclusions drawn from the premises based on the star test. There is no consensus on whether the conclusions presented are valid, and the discussion remains unresolved regarding the implications of the star test.

Contextual Notes

Participants note that the validity of conclusions may depend on the existence of the subject A, which introduces uncertainty into the application of the star test.

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I'm reading a book by Harry J. Gensler in which he introduces his 'star test' for checking whether or not a syllogism is valid. According to the star method the premises;

all A is B
all A is C

has no valid conclusion. But wouldn't;

some B is C

be a valid conclusion?
Sorry if this is kind of a silly question, I'm just starting to learn this stuff.
 
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Are you sure that you've copied it correctly? The closest that I could find was this fallacy - Undistributed Middle Term.

If the example is correct, perhaps the answer is elsewhere on that site.
 
I'm pretty sure. Gensler says the star test works by putting a star above any distributed letters in the premises and any non-distributed letters in the conclusion. The test says it is valid only if:
1) each capital letter is starred exactly once and
2) there is exactly one letter on the right hand side that is starred.
In the premises of the examples I listed 'A' would be starred twice, once in each premise, so that should make it invalid but I don't see why 'some B is C' isn't a valid conclusion.

The example I gave wasn't from the book, it was something I though up which fails the test but appears to have a valid answer.
 
Last edited:
Never mind, I think I figured it out. Is it because there isn't necessarily anything in A?
 
My first thought when I read your example was the following:

A = Ford
B = vehicle
C = 4 wheels

Substituting, using your example:
all Fords are vehicles
all Fords have 4 wheels

It looks like some vehicles have 4 wheels would be true.
 
But if we take:

A = fairies
B = things that have wings
C = things that have magic wands

then some B is C only if fairies exist, if they don't then there isn't necessarily something that's common to both B and C so I can't say with certainty that some B is C.
 
Wow, after I just posted I literally read two more pages and Gensler started to go into this, turns out it is because A may be empty.
 
Looks like we both learned something. :)
 

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