Potest aliquis timere timorem (ne scilicet immineat ei necessitas timendi, propter ingruentiam alicuius excellentis mali), quia provenit ex causa extrinseca, inquantum est passio quaedam consequens phantasiam imminentis mali.
It is possible for fear to be the object of fear (i.e., a man may fear lest he should be threatened by the necessity of fearing, through being assailed by some great evil), because it is due to an extrinsic cause, insofar as it is a passion resulting from the imagination of an imminent evil.
Illud solum habet rationem terribilis, quod ex causa extrinseca provenit; non autem quod provenit ex voluntate nostra. Timor autem partim provenit ex causa extrinseca, et partim subiacet voluntati.
Nothing has the formal aspect of fear, save what is due to an extrinsic cause; but not that which ensues from our own will. Now fear partly arises from an extrinsic cause, and is partly subject to the will.
Subiacet autem voluntati, inquantum appetitus inferior obedit rationi: unde homo potest timorem repellere. Et secundum hoc, timor non potest timeri, ut dicit Augustinus, in libro octoginta trium quaest.
It is subject to the will, insofar as the lower appetite obeys reason: wherefore man is able to drive fear away. In this sense fear cannot be the object of fear, as Augustine says (QQ. 83, qu. 33).