Universal Statements and Existential Commitment
Read section 2.16 (p. 126-128) to learn about a potentially counter-intuitive relationship between universal affirmatives and particular affirmatives – namely that the one does not imply the other. This is because universal affirmatives do not contain what is called an "existential commitment" that is, a statement that there is anything in the category the universal affirmative references.
Complete exercise 20, keeping in mind that universal affirmatives do not contain existential commitments. Check your validity answers against the key on page 225.