Critical reading always involves interpreting the author's key concepts, the ideas and terms that are central to the main points of the text. These concepts may be expressed in signal words or phrases. Sometimes the author will define or characterize key concepts. Some concepts must be interpreted from their role in the text.
When an author provides a definition, it is certain that this is an important concept to the text and one for you to make note of. Philosophical texts are not merely sets of instructions or information sheets that you can copy meanings from. They are efforts to express reasoned approaches to complex problems. Accordingly, be prepared to work at identifying and explaining key concepts.
Consider two examples that may help to point out ways that concepts can be identified and clarified from texts. Below are brief passages taken from two sources: one by Edward I. Koch, former mayor of New York City, and one from Stephan Nathanson, philosopher. Note that these are very brief excerpts provided for examples only. In context of the whole text there will be much more evidence to work from.
From these passages we can identify some key concepts that we need to get clear on in order to give an accurate account of each author's meaning:
Death penalty: Clearly this involves executing criminals. But which ones? In the United States people have been executed under various local or federal statutes for treason, sleeping on duty, and stealing horses. In some countries the death penalty is exercised for drunk driving, writing blasphemous literature, and adultery. Plainly, to make sense of either of the above passages we will have to determine how they intend to constrain the definition of this key concept. Otherwise, they might be talking about completely different practices. Developing alternate accounts of a concepts meaning can be very useful in building your interpretation.
Murder: Koch clearly distinguishes the death penalty from murder, since he says that the death penalty prevents murder. It is thus important to clarify the concept of murder as it is used here. One account might be that murder is the premeditated killing of one person by another. On that account, the death penalty would be a form of murder, too. Koch must mean something else by murder. Be prepared to use the entire text and even other relevant texts (e.g. writing by the same author) to build your interpretation.
Innocent: This word has different senses. On one sense, a person is innocent if they have not broken any law. On another sense, a person is innocent if they have not done anything morally wrong. On yet another sense, a person is presumed innocent unless found guilty by a court of law. On this last sense, no innocent people are ever executed by the US government, since the death penalty is carried out against those who are judged guilty. Whether they are innocent in the other senses is left open. You will need to study texts carefully to tell how a certain term it is being used. Don't suppose that your first impression or some common meaning is the whole story.
Deterrent: This term is not used in either passage, but it may be the best way to signify what Koch means by "protection" and what Nathanson means by "saving lives." Even from these brief passages, however, it is obvious that they are not talking about the same concept at all. Koch explicitly regards the death penalty as the only way to deter murders from killing again. Nahanson seems to have a broader notion of preventing murders from happening in the first place. Similar concepts may be expressed through different words. You may need to bring those different words together in a new account to make your interpretation clear.
Note that dictionary definitions will not suffice as accounts of how an author uses a concept. This is especially clear where different authors use the concepts in different ways. In that case, a single definition from a third source (dictionary) is irrelevant to the conflict. A dictionary is merely another text. In using a dictionary you must apply the same analysis and reasoning as you would with any sources.
Here are some steps you can take in your efforts to identify and clarify key concepts from a text: