The phrase "how to justify" is correct and usable in written English.
It can be used when discussing methods or reasoning behind a decision, action, or belief.
Example: "In this essay, I will explain how to justify the need for renewable energy sources."
Alternatives: "how to explain" or "how to support".
There is also disagreement over how to justify the use of drones.
It means that European politicians no longer know how to justify military expenditures to their people.
How to justify the iniquity of richer farmers in western Europe being paid far more than those in poorer central and eastern states?
Its curriculum has students pitching to potential users or customers and leading a monthly board meeting to learn how to justify themselves to investors.
How to justify the casting off of Freddy, who was fostered out, given no education or financial help, and made his living as a lathe turner?
The Agamemnon-Odysseus argument for and against the war is about how to justify war and whether one should behave like a criminal in order to win.
After all, how better to "justify the ways of God" to multiplex masses than through that most commercially rewarding medium of space battles?
How then to justify the company's turn to jazz composers and jazz-influenced dance in "Cross Roads" and "If Winter"?
Each discusses how trying to justify particular human values from the facts of evolution fails.
It seemed like he was using any hook, no matter how flimsy, to justify the Wall Street bailout that the Washington and New York elite pushed through.
In the digital ad world, it's about providing significantly more data in order to be able to measure and parse how ads perform, to justify how and where you will spend subsequent marketing budget.
