If the other person seems hesitant to open up, encourage them to do so by asking substantial questions. (inc.com)
The very substantial question that remains is who has the right to decide to enact that penalty? (canadianbusiness.com)
While it appears on the record before us that Amazon has carried its burden with respect to demonstrating the likelihood of success on infringement, it is also true that BN has raised substantial questions as to the validity of the «411 patent. (slaw.ca)