<p>First of all, to clear up some misunderstanding: During your first two terms, you wouldn’t need to change a class to pass/fail – any course you take during your first two terms are automatically and involuntarily pass/fail, even classes that cannot otherwise be taken for pass/fail.</p>
<p>As IMSAgeek mentioned, for a class that is not marked as letter only or pass/fail only, you can change the grading of a course to pass/fail or vice versa up until Drop Day. I do not agree with what IMSAgeek said about “required” classes. It is not even clear what is meant by “required”.</p>
<p>The class requirements that all majors have to satisfy include the math, physics, chemistry, biology, menu class, chem lab, additional lab class, writing, humanities, social sciences, and PE requirements. Of those, the required math, physics, and biology requirements which are meant to be taken after the first two terms are always marked letter grades only by convention. (Math, physics, and chemistry classes meant to be taken in the first two terms are marked as pass/fail classes, so they are pass/fail even if you had to re-take it later.)</p>
<p>Chem lab, PE classes, and freshmen humanities are marked as pass/fail only (so they are pass/fail no matter when you take them). The other classes: menu, additional lab, writing, humanities, social sciences, may or may not be marked letter grade only depending on the course. Starting in the 2011-2012 catalog year, advanced humanities and advanced social sciences requirements cannot be fulfilled by pass/fail; this did not apply to people on previous catalog years.</p>
<p>A few departments are listed in the catalog to have graduation requirements that say classes taken on pass/fail may not be used to satisfy some or all of the option requirements. Other majors do not seem to have such a requirement, though I am not familiar with how they work. (Of course, that doesn’t mean you can’t take them on pass/fail; just that you can’t use them to satisfy the requirement.)</p>
<p>There are other rules on pass/fail, like only up to 90 units of classes <em>elected</em> to be taken on pass/fail can be used for degree requirements (including the 486 total units requirement). (You can take more; they just can’t be used to satisfy requirements.) 90 units = 10 regular classes that count for your degree can be elected pass/fail. That means, for example, prior to the 2011-2012 catalog year, you can take all your humanities and social science requirements on pass/fail (which is 108 units, but 18 units are freshman humanities which are always on pass/fail, leaving 90 units which you can elect), if you so wanted.</p>