How could William Jennings Bryan oppose the gold standard and also support bimetallism? Bryan took each position at a different point in his career, with his support for bimetallism coming later in life.
Bimetallism called for a fixed value for gold, which was the opposite of the gold standard.
Bryan spoke in favor of the gold standard when addressing the wealthy and in favor of bimetallism when speaking to the poor.
Bryan opposed the idea of a fixed value for gold while supporting the concept of a currency based on two metals.