03 / 18 · Read the argument
The missing bridge
Expose missing assumptions without quietly treating them as facts.
Builds on True is not the same as valid
Go to practice ↓A question to keep in mind
'It is faster, so we should use it.' What has been left out?
Real arguments often omit a bridge from the stated evidence to the conclusion. 'This tool is faster, therefore adopt it' also depends on priorities, accuracy, cost, and compatibility with existing work. A premise about what is the case does not by itself determine what should be done.
Make a proposed bridge explicit and label it as an assumption. Adding it may repair the deductive form, but does not establish its truth. Prefer a limited bridge you can test over a sweeping rule that makes the conclusion automatic.
Look for a plausible situation where the stated evidence holds but the decision changes. This reveals missing conditions. Do not pretend your reconstruction is the speaker's exact intention; it is a candidate to confirm.
Work through an example
- Claim: 'Package A takes half the time, so migrate.' Counter-situation: it does not support a file format needed for the task.
- Candidate bridge: choose the faster option among those meeting the same correctness, compatibility, and budget requirements.
- The migration now also requires evidence that A meets those requirements. The word 'faster' did not supply it.
Your turn
0 / 3'This plan has the highest expected revenue, so choose it.' Which assumption most directly bridges the gap?
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Revenue is the only decision criterion once constraints are met.
A bridge can be logically helpful and substantively debatable at the same time.
'Students using this app score higher, so the app raises scores.' What should be investigated first?
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Whether users already differed in motivation or prior ability.
We return to causal evidence in lesson 16. Here the task is to expose the extra assumption, not calculate an effect.
You add a missing premise and the form becomes valid. Is the argument now sound?
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Only if all premises, including the new one, are true.
This is the validity/soundness distinction from lesson 2, now applied to a repair.
Bring it back to your own work
Revisit your recommendation from lesson 1. Add one missing bridge, then write what evidence or agreement would justify it.
How do I retain independent judgment when using AI here?
Keep your own answer before consulting an AI candidate. Check sources, calculations, inference and conditions; explain adoption or rejection. Then solve a new-context task independently and apply the checks to this lesson.
Practice the verification workflow and keep a recordMy learning status
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