A simplified definition of internalism is this: an internalist believes that a person must be aware of his justification for P in order for his belief in P to be justified. I believe this is the simplest definition of internalism that most internalists would use. However, this is not the whole story. Internalists vary with respect to at least 3 important issues: grounds, adequacy, and basing. A person may be an internalist about grounds, but not about adequacy and basing. A person may also be an internalist about grounds and adequacy, but not basing. A person may be an internalist about all three, or just grounds and basing. This article will provide a simplified explanation of the concepts of grounds, adequacy, and basing and will provide examples to make these concepts clear.
Furthermore, an internalist may be an infalliblist with respect to grounds, adequacy, and basing. This article will briefly mention the infalliblist view with respect to all three. The purpose of this article is not to refute internalism, but to help both externalists and internalists think more clearly about internalism.
The following accounts of grounds, adequacy, and basing will most likely be slow reading, but will make important distinctions that I think are worth thinking about.
For some people, it is necessary and/or encouraging to remember why such questions are important and how they affect our day to day life. Please indulge me in a bit of quick cheerleading because readers sometimes need to be riled up before they can read through a technical article. For the Christian, thinking clearly about these issues helps us to answer questions of biblical exegesis, it helps us in daily apologetics, and it helps us answer day to day questions. Romans 1 teaches that all men, including unbelievers, “know God”. Does this mean that unbeliever knows that he knows God? Or, could it possibly mean that he has a kind of suppressed knowledge deep down inside and is totally unconscious of it? As another example, Jer. 17:9 teaches that nobody knows their own heart. Does this mean that a person could know something without realizing they know it? These questions also bear on daily apologetics. In the same vein, your defense of your faith will look different if you are witnessing to someone who is consciously suppressing his belief in God versus someone who seems very open to Biblical truth, but simply doesn’t yet agree or doesn’t know very much about the Bible and so, refuses to accept it. Thinking clearly about these questions also can help us day to day. Often, we ask the question: “How do I know that?” Sometimes, this is a hard question to answer. But, if you can’t answer, does that imply that you don’t actually know it? Or, could you know it but have simply forgotten how you know? Or, could you know it but have never been aware of how you know in the first place? Internalism suggests answers to all of these questions, but it is a tricky sticky subject. If you are into this kind of thing, proceed slowly and carefully and please try and correct me in the comments section on anything you think I’ve gotten wrong.
An internalist about “grounds” believes that, in order for P to be justified, one must believe that there is a reason for P and he must be aware of that reason.  So, in order for Otis to be justified in believing that there is a goat in his room he must also believe two other things. He must first believe that he has a reason to believe that there is a goat in his room. Second, he must also be aware of that reason. So, the internalist about grounds will say that for Otis to be justified in believing that there is a goat in his room, he must also believe that he has a reason for believing there is such a goat and he must be able to identify the reason; such a reason might be that he sees a goat-like figure eating all his shirts (as goats often do). If a given internalist defines justification infalliblistically, he will probably also be an infalliblist with respect to grounds. An infalliblist with respect to grounds would change the word “believe” in the above definition to “know infallibly.” So an infalliblist would say that in order for P to be justified, one must infallibly know that there is a reason for P and he must infallibly know that reason.
You might ask: What if the reason for believing P is a poor reason? What if Otis believes there is a goat in his room because his brother, an infamous lying trickster, told him so? These are questions of adequacy.
An internalist about “adequacy” is like an internalist about “grounds” except that he believes that the “grounds” for a belief must be adequate to support the belief in P. So, if Otis believes there is a goat in his room because his brother, an infamous trickster, told him so, then the internalist about adequacy would say that Otis is not justified in his belief that there is a goat in his room.
An alternative form of internalism about adequacy is the view that a person must merely believe that his grounds are adequate to support his belief in P. Whether or not the grounds are actually adequate is not relevant for this type of internalist. So, in the example just given, Otis could be justified in believing that there is a goat in his room because his brother, an infamous trickster, told him so. If Otis believes that these are adequate grounds, this form of internalism about adequacy would affirm that he is justified in believing that there is a goat in his room.
Infalliblism about adequacy would simply say that the reason for the belief in P must be a deductively valid syllogism and that the premises must also be infallibly justified. Falliblism about adequacy simply says that the reason for the belief in P might also be a strong inductive argument with premises that are also probably true.
An internalist about “basing” believes that, in order for P to be justified, the belief in P must have been “caused” by belief in the grounds for P. So, if Otis believes there is a goat in his room because he believes that all toads are amphibians, an internalist about basing would say he is not justified in believing this, even if he has some other strong grounds that actually do support his belief that there is a goat in his room.
An alternative form of internalism about basing says that, in order for P to be justified, the person must merely believe that his belief in P was caused by his belief in the grounds for P. So, this type of internalist would say that Otis could be justified in believing that there is a goat in his room because all toads are amphibians so long as he believes that his belief about the goat is caused by his belief about the toads.
An infalliblistic conception of internalism about basing would say that, in order for P to be justified, the person must infallibly know that his belief in P was caused by his belief in the grounds for P.
A Christian Example
Sam, and other people, often want to know whether or not they know God. An internalist about grounds would ask Sam: Can you provide your reason for your belief in God? If Sam says “no, I just know God,” an internalist about grounds would conclude that Sam does not know God. But lets say Sam provides his reason and satisfies the internalist about grounds. An internalist about adequacy would also require Sam to show that his grounds are sufficient to support his knowledge of God. If Sam could not show that his grounds are adequate, then the internalist about adequacy would conclude that Sam does not know God. An internalist about basing would ask Sam to show that his grounds caused him to believe in God. If Sam couldn’t show that his belief in God was caused by his grounds, the internalist about basing would conclude that Sam does not know God. This is not to say that these internalists would conclude that Sam does not believe in God. They would simply conclude that he has no epistemic justification for his belief in God, so he cannot “know” God.
I have tried to clearly represent three major categories of internalists by stating their views and giving clarifying examples. I trust that this will not be new to some people, but I also think that most of the philosophers that I interact with on a daily basis will be very glad to ponder these distinctions. I, personally, am not an internalist. This is why I have taken it upon myself to learn about the various forms of internalism so that I can better understand the view I currently reject. For a more detailed discussion of these distinctions, see chapter 1 of Epistemic Justification by Richard Swinburne.
 For clarity, this is a discussion of internalism with respect to epistemic justification.
 Some forms of internalism say that a person need not actually be aware of this reason but must be able to become aware of it simply by trying to become aware of it. So, upon this view, you might be justified in believing that you are reading this article without being conscious of your reason for believing this. But, when asked, you would be able to give your reasons for thinking you are reading this article. Most of the same distinctions given in this article apply to this view, but this distinction will not be discussed.