Islam has forbidden us from following any path other than the path of ‘Ilm (knowledge): ‘And follow not that of which you have no knowledge. Verily! The hearing, and the sight, and the heart, of each of those you will be questioned (by Allah).’ 
From this it becomes clear that the basis in every matter of the Sharee’ah, whether we are ordered to do something or forbidden from a matter, is that we should arrive at knowledge of its hukm through one of the paths of knowledge. If the mukallaf (legally responsible) is unable to do that, then he is obliged to study the matter to arrive at a preponderant view in an issue.
Taqleed does not bring us to any definite knowledge or preponderant view; and that is why many scholars did not allow it, except for the weak and compelled. He is the layman who does not have the tools of ijtihaad. This is what they obliged and permitted him to ask for a fatwa and imitate that.
As for the rest, the basis is they should exert the effort to deduce the Hukm, this is better to do, though it is allowed for them to make taqleed as we have clarified previously.
Those who do not have the ability for ijtihaad are of two types:
1. The follower (muttabi’). He is the one who has knowledge of the some of the recognized disciplines in the Sharee’ah but it is not enough for him to make ijtihaad. That is why it is allowed for him to make taqleed, but with knowledge of the daleel used by the Mujtahid he follows.
2. The layman who does not have even some of the recognized disciplines in legislation, for him the fatwah of an Imam is sufficient. He can ask him for hukm and get an answer as to either it is halal or haram…
The question which arises is: If the Muqallid makes taqleed in a specific matter; is it allowed for him to make taqleed to someone else in the same matter?
The answer is that the Hukm of the Sharee’ah in respect to the muqallid is the hukm shar’i that has been deduced by the mujtahid he is making taqleed to. This means the issue is as follows:
1. When the action of the muqallid is linked to the issue (mas’alah) he has imitated, then it is not allowed for him to follow another rule, because he has bound himself to a Sharee’ah rule and acted upon it.
2- If, however, his action is not linked to that issue, then he can follow someone else.
Definition of mas`alah (issue): what is meant by mas`alah is every action or actions, which have no more other (actions) that depend for their correctness on it (mas’alah).
As for a part of the issue, it is any action, which is necessary for the correctness of the issue, such as the shuroot (conditions) and arkaan (pillars).
Wudu: It is actions, upon which the correctness of other than it depends. . This is because the correctness of Salah depends on wudu; and therefore wudu is not a mas`alah according to the definition, but considered a part of the salah, for it is necessary to insure the salah is correct.
Salah: It is actions upon which other things do not depend. Thus, it is a mas`alah. Anything that is necessary for the correctness of the salah is considered part of the salah, such as the pillars (arkan) and the conditions (shurut) of siHHat (correctness), like purity (tahaarah) and facing the Qiblah.
The niyyah (intention) of fasting: It is an action on which the correctness of something else depends. The correctness of the fast depends on the intention. That is why the intention (niyyah) is not a mas`alah but part of another mas`alah.
The fast (al-sawm): It is an action on which nothing else depends for its correctness. It is a mas`alah. Anything that is necessary for its correctness is considered a part of it, such as the intention (niyyah) and abstinence from food. So, if a person followed a mujtahid in salah, then he should follow all of its parts, such as wudu (ablution), bath from major impurity, Tayammum (dry ablution), facing the Qiblah and the arkaan of the Salah. If he has followed a mujtahid in fasting, then he must make taqleed in all its parts, such as the intention (niyyah) and the obligation of making it fort every day or for the whole month, is it correct to make the niyyah during the day or should it be made during the night, muftiraat (what breaks the fast) and the dispensations for breaking the fast (rukhsas). However, it is allowed to follow a mujtahid in another matter.
All of this applies as long as the person is a muqallid (a follower); but if he acquires the ability to judge the evidences and to outweigh them, in this case, it is allowed for him to leave the mujtahid he made taqleed to and follow the stronger daleel.