I learned 去年 well before 昨年, so I just always use 去年 out of habit. But now I'm wondering if they really are interchangeable or if there's even a subtle difference that would make one more appropriate in some situations over the other.
So are they interchangeable, or does a subtle difference exist?
去年 can be used in almost any situation. 昨年 is more formal and not good for casual conversation.
For example,
1) 去年、結婚いたしました。
2) 昨年、結婚いたしました。
2) is better because いたしました is a humble form but 1) is totally acceptable. On the other hand,
1) 去年、結婚しちゃった
2) 昨年、結婚しちゃった
1) is natural but 2) sounds a bit strange.
The same applies to:
昨日{きのう} vs. 昨日{さくじつ} (yesterday; the same kanji but read differently)
前年{ぜんねん} is a similar word and it means 'previous year'.
大統領{だいとうりょう}選挙{せんきょ}の前年は、株価{かぶか}が上がる。
Stock prices rise in a pre-presidential election year.
前年 is often used to compare a certain year with the previous year.
前年比{ぜんねんひ} 50%増{ぞう}
Up 50% over the previous year
Without reference to another year, 前年 means 'last year' and it is used almost always to compare 'last year' with 'this current year'.
1) 息子が生まれる前年に、結婚しました。(I got married in the year before my son was born.)
2) 前年、結婚しました .
1) is natural. 2) sounds incomplete because it doesn't compare anything or specify the reference year.
From what my teacher told me, 去年{きょねん} and 昨年｛さくねん｝mean the same thing, but 昨年 sounds more sophisticated.
I would guess that depending on the situation they may or may not be interchangeable with the difference being who your audience is.
There may be a situation where this specifically is the case, but I am not aware of it, someone more knowledgeable than I will have to answer as to whether or not this is the case.
