A quote on the endeavor of Ijtihad in Islamic Law

Hamza Yusuf writes in his historical-juristic essay on the rulings of Islamic law on chess:

Contrary to the Orientalists’ claims that the gates of ijtihad were closed in the ninth century CE, ijtihad has always been an active endeavor of the community of jurists throughout the Muslim world.[4]

In the foot-note # 4, he writes:

The only closure—if there was one—was on what is known as “absolute ijtihad” that historically was achieved by a handful of scholars in the early part of Islam and later considered impossible to achieve. However, although many consider this door closed and locked, it has always been viewed as a door that is possible for one to enter, if one has the key. [Emphasis added.]