1.why is exposure a subjective decision?
2.how do our decisions about aperture and shutter speed influence the photography that we take?

w. eugene smith said, “up to and including the moment of exposure, the photographer is working in an undeniably subjective way. by his choice of technical approach, by the selection of the subject by his decision as to the exact cinematic instant of exposure, he is blending the variables of interpretation into an emotional whole.”

post detailed answers to the questions above. u.

1.Why is exposure a subjective decision?  

Exposure is the amount of light you let in the camera to take the picture.  If you let in lots of light, the resulting picture will be bright and if, on the other way, you left only a little bit of light in the camera, the picture will be dark.

Although the camera could select the perfect exposure for a given photo, to enhance most/all details, the photographer should intervene to decide the amount of the light he wants in... to control the overall feeling/ambiance of the photo.  It's his photo, a second photographer might come in and make different decisions regarding the exact same location and composition.  Just like a painter will approach the empty canvas its own personal way.

2.How do our decisions about aperture and shutter speed influence the photography that we take?

Aperture and shutter speed are the tools used to control the amount of light in the camera, the exposure talked about in previous question.

The best way to discuss this is to take a classic example.  Imagine you want to take a photo of a fountain or a small waterfall.  There is movement there.  Is it better to take a photo with a very fast shutter speed to capture individual drops flying in the air, freezing the time?  Or to do a long exposure to show the flow of the water?  Maybe somewhere between those two extremes?  All these answers are good and depend on what the photographer wants to transmit as message.  That's where the subjectivity comes into play.  As you play with the shutter speed, you also need to adjust the aperture to control the overall exposure of the photo.