The phrase "I further think" is correct and usable in written English.
It can be used to express an additional opinion or thought in a discussion or argument.
Example: "I believe that the project will succeed; I further think that it will exceed our expectations."
Alternatives: "I also believe" or "I additionally think."
I further think that unless we clean up our own house, Republicans are going to clean that up for us, in the fall.
"I further think that one reason why [football's abuses] are not remedied is that so many of our people whose voices would be potent in reforming the game, try to abolish it instead".
"I further think that he is going to run for president, and he is going to create something".
And I further think that the 2008 election may very well have delayed the emergence of the Occupy Movement by three years.
I further thought that without quite realizing what had happened to them, the people at the S.E.C. were now lighting out after the very people -- the average American with a bit of money to play with -- whom they were meant to protect.
I didn't give it further thought until I opened this morning's papers and saw three MPs and a Tory peer all over some front pages.
"I'd like to know if the public want this practice to continue or whether I need to give it further thought," Mr Salmon said.
Before I go any further, I think I should explain where I'm coming from so as to cast aside (or perhaps, affirm) any suspicion that I'm simply an Android fanboy.
After further thought, I do think the complaint was valid and therefore I have included retrospective mentions of the paper in order to make its provenance crystal clear.
"Even though the presidents went further than I did, I think I kept pace with them".
In fact I'd go further: I think even the most moral moral absolutists cannot be as moral as the most moral moral relativists.
