I just want to point out my position on a few statements. The first is about truth and a clarification on my position to head-off any claims I may get saying that I hold 'relative truths'. Below I will give you a quick run-down on how I see truth.
Truth as a topic is deep and worthy of as many hours as one can spare to study it, I must confess that I have only read half a dozen books pertaining specifically with this topic. I do spend a lot of time thinking about the concepts and what it means for my life, I believe this process helps to reinforce and order my readings into a steady, manageable flow. Anyway, I treat the idea of truth in this way:
A) Fish live in water
This proposition is true. What does it mean to say that this proposition is true? It means, simply, that this is the way things are. To say that the proposition is true is to say nothing more than: yes, fish do live in water. Thus, consider the proposition that says that (A) is true:
B) It is true that fish live in water
(A) and (B) are equivalent in the sense that, necessarily, if (A) is true then so is (B), and if (B) is true then so is (A). In other words, to say that it is true that fish live in water comes to the same thing as saying that fish live in water. Used in this way - which is all that is needed for logic and critical thinking - the word 'true' is no more mysterious than the words occurring in this sentence: 'Fish live in water'. In this sense you cannot doubt that there is 'really' such a thing as truth, or that truth is knowable, any more than you can doubt that fish live in water. This is a 'known truth'.
Discomfort and misconception with the word 'true' is sometimes due to a failure to distinguish truth from 'belief'. In saying that 'it is true that fish live in water', I show that I believe that fish live in water (presumably because I know that fish live in water). Yet clearly the truth of this proposition has nothing to do with what I believe. That depends only on how things stand as regards fish, and what fish do does not depend on what people think. So despite the fact that I used the word true to assert the above, the truth of what I asserted does not depend on my beliefs in any way.
In other words there is a difference between believing that something is the case and knowing something is the case. There is a deep-seated myth that what is true depends on nothing more that personal opinion or taste. There is no way to make satisfactory sense of the relativity-myth. Truth is not relative, it is objective, and the truth of a proposition is independent of our desiring or believing it to be true. Just as desiring or believing cannot make there be a 'god', desiring or believing cannot make it true that there is a 'god'. To believe is to believe something to be true, but truth is not the same thing as belief. This means that truth is independent of all of us; it does not mean that one powerful person or being could hold the key to all that is true about the world. The aim of good reasoning is to get at the truth, at the way the world is, irrespective of how people think or feel it to be. Rationality is a great leveler. In the pursuit of truth we are all equally placed before the world, and no amount of power can provide an advantage.
Of the four stances we can take towards a proposition - believing it, not believing it, suspending judgment, not engaging with it - the first two admit of degrees. There are many positions on a scale that one can believe something to be true or disbelieve it. However, the fact that someone may be perfectly rational and justified in holding a belief does not establish that the belief is true. A belief's being true is a matter of its fitting the facts, not of there being good reasons to think that such-and-such is the case.
Knowledge and truth are intimately linked. If someone knows something then the proposition known must be true: one cannot rightly say that fish live in water if fish don't live in water. The truth of a belief is certainly one necessary condition of that belief's being knowledge. But it is not enough, there are further necessary conditions for one's belief to be true and, ultimately, knowledge. In particular, a true belief counts as knowledge only if we arrive at that true belief via the correct route: We have knowledge only if we have good reasons for holding a belief that turns out to be true. We have to be justified; we need to have solid evidential support. We must, if you like, earn the right to be so sure. Lucky true beliefs do not count as knowledge.
Therefore, if someone says to me that "there is life after death" or that "the bible is literally true", it would be a mistake to retreat into relativity and conclude that their belief is 'true for them'. The particular belief is false, that's that. Indeed, such people can sometimes paradoxically be described as believing that which they know to be false - or self deceived. However, I shouldn't be so cold-blooded. It's not usually the case that such people are intentionally deceiving themselves, but rather that they are trying to deal with their plight by having faith that their hopes (however unlikely) will be borne out. So it’s rather unfair and unfeeling to accuse such people of being irrational, even though strictly speaking they are. While we should try to avoid irrationality, we must also accept that as human beings, it is sometimes psychologically better for us if our beliefs and behavior fall short of rationality. I suspect, and there is a growing body of research to suggest, that this is a major reason that people choose to accept the notion of the afterlife and god. However, I will suspend judgment on this until more evidence arrives.
Absolute truths only exist in the formation of the account of knowledge known as the tripartite account, according to which: to know that P is to have a justified true belief that P. My truths are of course gleaned from the processes above. Provisional truths are important because they supply us with an ever-sharpening account of how the world is. I tend to stay shy from declaring absolute truths; I’ll leave that to the preachers and politicians. The truth specifically regarding the evolution can be laid out a theory or theories. I'll be brief as to what theories are and how they claim to be truth.
Saying that evolution is 'just a theory' (a common remark) seems to belittle theories as something subjective - to dismiss them as merely someone's opinion. Properly understood, however, the term 'theory' has a specific meaning that contrasts scientific hypotheses with less methodologically sound and evidence based views about the way the world is. To say that something is a theory is not to cast doubt on its objectivity in any way; we speak, for example, of the 'theory of calculus' in mathematics or the 'theory of gravity' in physics, without meaning to cast doubt on the theories or the reliability of their resulting applications, as for example in the building of bridges. Nor is calling something a 'theory' to mark an invidious distinction from facts; a theory is a system of propositions concerning some domain of facts, such that if true then it is a correct account of those facts. True propositions are never themselves identical to the facts they are about or represent.
In general, a scientific theory posits a hypothesis that is testable, and those tests are able to be carried out in a way that makes them perspective-free; that is, they are able to be carried out by anyone able to observe the results and use any measuring apparatus competently. Evolutionary theory counts as a scientific theory on this account, and, again, to say that it is a 'theory' does not itself mean that there is something doubtful about it. Its hypothesis about the diversity and history of life and the processes therein, can be, and has been for over 150 years, exhaustively tested using data provided by scientifically respectable methods such as radioactive dating and DNA testing. By contrast, creationism, which also seeks to explain the diversity of life, is not a scientific theory by these lights because the faith-based account of creation it presents is not testable by such means. Theories supply us with explanations and interpretation of an incredible amount of data in our world. Using the reasoning outlined above, we can arrive at truths about evolution easily. In fact one can do a good deal of proving hypotheses at home using only some of the scientific tools available.
excerpts from Critical Thinking, 2010