What is the difference between supplication for someone present and supplication for someone absent, what are the conditions for each, is everyone who supplicates for someone absent committing shirk, and what is the ruling on saying "Ya Ali" or "Ya Hussein"?

The answering of supplications requires not only power but also knowledge. It is forbidden to ask of other than Allah that which only Allah is capable of. As for that which someone other than Allah is capable of, one should ask a living, present individual; because the absent—especially the deceased—does not know the servant's condition or request, and asking them implies a claim to knowledge of the unseen. Asking that which does not contradict Allah's exclusive knowledge of the unseen is permissible, such as asking a present person or using modern communication methods. The fundamental difference between the present and the absent is the possibility of knowing the servant's condition. Supplication to the absent may occur in the form of seeking aid and requesting benefit or averting harm, and this is shirk (polytheism). It may also occur in the form of seeking intercession (tawassul), which is a reprehensible innovation (bid'ah). However, if it is in the form of eulogy (recalling the deceased's virtues), it is permissible if sincere. The Quranic verses that condemn polytheists for supplicating idols are used to condemn anyone who supplicates other than Allah concerning that which only Allah is capable of, due to the prohibition of shirk. There are other general verses that prohibit supplicating other than Allah, such as His saying, the Almighty: "And do not invoke besides Allah that which neither benefits you nor harms you" [Yunus: 106].