Final answer:
The qualifier component of Toulmin's model expresses the degree of certainty that the arguer feels about the claim.
Step-by-step explanation:
The component of Toulmin's model that expresses the degree of certainty that the arguer feels about the claim is Qualifier. The qualifier determines the strength of the claim by indicating the level of confidence the arguer has in the assertion. It helps to convey the arguer's attitude towards the claim and acknowledges any limitations or exceptions. For example, a qualifier like 'probably' or 'likely' indicates a moderate level of certainty, while a qualifier like 'certainly' or 'without a doubt' indicates high certainty.