Cannot convert method group 'xxxxxxxxxxx' to non-delegate type bool.

New to programming and need help with an error at line 10; Cannot convert method group 'xxxxxxxxxxx' to non-delegate type bool. I'm learning from this tutorial page.

public class PlaceMonster : MonoBehaviour {

 public GameObject MonsterPrefab;
 private GameObject Monster;

 private bool canPlaceMonster()
 {
     return Monster == null;
 }
 void OnMouseUp()
 {
     if (canPlaceMonster) ())
             {
         Monster = (GameObject)
             Instantiate(MonsterPrefab, transform.position, Quaternion.identity);
         AudioSource audioSource = gameObject.GetComponent<AudioSource>();
         audioSource.PlayOneShot(audioSource.clip);
     }
 }

}