AUTHOR:Shaikh Muhammad ‘Umar Bazmool
SOURCE: At-Ta’seel fee Talab-il-‘Ilm
The Ninth Foundation:
People are divided into two categories with respect to knowledge: (1) Those who know, and (2) those who don’t know.
Those who don’t know are obligated to ask the people of knowledge and accept their statements, while expending what effort they can in order to know the proofs and evidences.
Allaah says: “And We did not send before you anyone except men that we gave revelation to. So ask the people of remembrance (knowledge) if you don’t know. With clear signs and books (We sent the Messengers). And We also sent down unto you the Reminder (i.e. Sunnah) so that you may explain clearly to the people what was revealed to them (i.e. the Qur’aan), and that they may give thought.”[Surah An-Nahl: 43-44]
The one who knows the religious ruling on an issue, based on its evidences, is from those who know. So he is a person of knowledge (‘aalim).
And whoever takes the opinion of someone else without knowing its proof, he is a blind-follower (muqallid), and not a person of knowledge. Ibn ‘Abdil-Barr relayed the consensus (Ijmaa’) that the blind-follower – who is the one who accepts the opinion of someone else without knowing its evidence – is not from the scholars.
And as for the one who knows an issue based on its evidence, while investigating the different views and proofs used on the issue, while taking the view that appears most correct to him, then he is aMujtahid.
As for the one who has knowledge of an issue based on its evidences, meaning that he has accepted the view for which the proofs are most convincing to him on that issue, without making efforts into examining or looking into the other (differing) opinions. So he only has knowledge of the most correct view based on its evidences. This person is a follower (muttabi’).
If the Mujtahid is one who abides by this methodology in all of the issues of knowledge and doesn’t restrict himself to just looking into the principles of one specific madh-hab, then this person is an absolute Mujtahid.
If he limits himself to investigating an issue by only looking into the principles of one particular madh-hab, then he is a limited Mujtahid.
So if his condition is that he performs Ijtihaad in all of the issues of the Religion, then he is a completeMujtahid.
And if his condition is Ijtihaad in just some issues, apart from others, then he is a partial Mujtahid. So with regard to an issue, a person can be a Mujtahid implementing partial Ijtihaad, and some another issue he could be a muttabi’ (follower), and yet in another issue, he could be a muqallid (blind-follower). This varies according to what is easy for him during the occurrence of an event that this issue relates to.
One must also beware of opinions. This refers to statements in the Religion of Allaah that have no authentic or considerable evidences.
You must also know, my brother, that the Qur’aan and the Sunnah serve as the foundation for opinion and they act as the standard by which opinion is determined. The opinion is not the standard used to determine the Sunnah. Rather, the Sunnah is the standard used to determine the opinion. So whoever doesn’t know the foundation will never attain the branch.
Ibn Wahb said: Maalik narrated to me that Iyyaas bin Mu’aawiyah said to Rabee’ah: “When something is built upon crookedness, it will never be able to straighten itself.” Maalik said: “He means by this, the Muftee that speaks based on a foundation, which he builds his speech on.” 
Ash-Shaafi’ee, may Allaah have mercy on him, said: “Whoever learns the Qur’aan, his value becomes magnified. And whoever speaks about Fiqh, his status becomes increased. And whoever records Hadeeth, his arguments become strengthened. And whoever looks into accounting, his views will become unerring. And whoever does not maintain himself, his knowledge will not benefit him.” 
Ibn Hibbaan, may Allaah have mercy on him, said: “Verily, in adhering to his Sunnah (sallAllaahu ‘alayhi wa sallam) there is the most complete form of salvation and the most comprehensive form of nobility. Its lights cannot be doused nor can its arguments be refuted. Whoever adheres to it will be protected, and whoever opposes it will be condemned. This is since it is the stronghold and the firm support, whose merit is clear and whose rope is solid. Whoever holds onto it prevails and whoever opposes it becomes destroyed. So those who stick to it will be successful in the next life and blessed amongst the creatures in the present life.” 
 Jaami’ Bayaan-il-‘Ilm wa Fadlihi (2/166-172) with some very light abridgement and adaptions.
 Siyar A’alaam-in-Nubalaa: 10/24
 Saheeh Ibn Hibbaan (Al-Ihsaan): 1/86