The Rulings of the Shari'ah Apply Only to what is Outwardly Visible
At this point, another aspect can be mentioned, which leads some Muslims to an excessive application of takfir:
The lack of understanding that rulings in Islam naturally apply only to what is outwardly visible and demonstrable. No person can independently know what is in another's heart, which is why every Muslim is obligated to judge only based on external appearances. For this reason, the rulings of the shari'ah are always based on perceptible actions and statements.
Thus, it is naturally possible that a person outwardly grows up as a Muslim in an Islamic society while, in reality, not having understood tawhid at all. Likewise, it is conceivable that such a person, due to his ignorance, eventually practices polytheism. However, as long as this remains unknown to others, the person can clearly only be regarded as a Muslim by other people.
On the other hand, it may be that the person has not inwardly accepted Islam, even if he does not outwardly display this. In this case, Islam is rejected internally, while externally, the pretence of being a Muslim is maintained. Such a person is referred to in Islamic terminology as a munafiq/hypocrite. The phenomenon of the munafiq is frequently addressed in Islamic sources and is well known, which is why the term appears numerous times in the Qur'an.
In some hadiths, it is also indicated that there are certain signs that warn the Muslim to be cautious of hypocrisy. However, according to Islamic teaching, it is not permissible to accuse someone of kufr unless a clear action or statement of kufr has been observed from this person.
Additionally, in certain cases, it may be that the person said something that contradicts Islam but is excused due to ignorance – some brief remarks on this will be given in the following.