Where do I put commas in this sentence? (Brains change shape but some people still believe that they aren't malleable.)

Brains change shape, but, some people believe that they aren't malleable.

both the address and the poster use diction to convey their message. diction is defined as a style of writing or speaking based on the types of words chosen in order to send a message. parallelism is when a similar sentence structure is used for several sentences on a text; roosevelt's address doesn't follow that. repetition has to do with repeating a word or sentence in order to emphasize and idea, however neither the poster nor the address use repetion. finally, the address doesn't use images to convey a message.

onto a large boat, and mark the water level that the boat sinks to. then, take the elephant out and put a bunch of marked weights onto the boat until it reaches the same water level. add up the masses of the weights to get the weight of the elephant.