Wiktionary
vb. 1 (context obsolete English) To be right. (15th-18th c.) 2 To have grounds, justification etc. ((term: to) do something, or (term: for) something).
Usage examples of "have reason".
We suffer not only the evils that actually befall us, but all those that our intelligence tells us we have reason to fear.
If this should happen we shall have reason to bless its inventors.
If those experiments were successful, then the celebrations would begin in earnest, and merely wary adversaries would now have reason to fear the Tholian Assembly.
Our arrival, I have reason to believe, was an event in the old town.
And that the great monster is indomitable, you will yet have reason to know.
We have reason to believe that you are running illicit weapons to the Maquis.
I have reason to believe that she has been at one time or another in your establishment at Bournemouth.
I don't know precisely what was preserving those fellows, but I have reason to believe that now they've been exposed to air, their cell structure may begin to break down and they'll start to decay.
For we find that you have said or done such and such (naming them), wherefore we have reason, in the opinion of the said learned men, and compelled thereto by your own excesses, to judge you as a backslider according to the canonical decrees.