The third level is actual intellect (bi-l-fiʿl): a developed capacity to derive conclusions from established principles, even when every conclusion is not presently being considered.
The fourth is acquired intellect (al-ʿaql al-mustafād), described in terms of the presence of intelligibles and a more complete realization of understanding.
Intellect by disposition means readiness through elementary knowledge; actual intellect means a formed power available for reasoning; acquired intellect concerns the present realization of intelligible knowledge. Possessing an ability is not identical with consciously entertaining every proposition it could produce.