"I think" is a statement of cursory conclusion, while "I believe" indicates a more deeply considered and committed position. Note that someone may say "I think" when they actually mean "I believe", simply because it might be received as less confrontational. "I reckon" carries an ever lower level of assertion than "I think", (or perhaps an even higher level of conciliation).
They're pretty much synonyms, but I would argue that the longer word is actually more readily understood by the general populace (at least in America), despite what NGrams may tell you.
First of all, pretension is a more bookish term, so it would not surprisingly show up more in books. That does not mean it shows up more in speech or casual writing (especially online writing).
Second, pretentiousness is a noun made from the adjective pretentious, which virtually everyone knows and understands. You will hear the word used everywhere from literary soirees to shopping mall get-togethers to trailer-park barbecues.
Now, it is likely that most people would understand pretension if they stopped to think about it. They just wouldn't say it.
All right, having said that I am obliged to point out that pretension is much the better word to use with a complement. For example:
My wife can't stand her pretensions to culture.
You can't really say "pretentiousness to culture"; it just doesn't work.
And by the way, you won't hear the phrase "pretensions to culture" in a trailer park, unless said park caters to graduate students.
Best Answer
Surname and last name both imply position, assuming a construct of "given name, family name". This doesn't work in countries that reverse this to "family name, given name", like China. Using "family name" and "given name" avoids the confusion of having last names first and first names last.