The idea of truth as objective is simply that no matter what we believe to be the case, some things will always be true and other things will always be false. Our beliefs, whatever they are, have no bearing on the facts of the world around us. That which is true is always true even if we stop believing it and even if we stop existing at all.
Most people in most cases certainly act as though they believe that truth is objective, independent of them, their beliefs, and the working of their minds. People assume that the clothes will still be in their closet in the morning, even though they stopped thinking about them during the night. People assume that their keys may really be in the kitchen, even if they dont actively believe this and instead believe that their keys are in the hallway.
Why adopt such a position? Well, most of our experiences would appear to validate it. We do find out clothes in the closet in the morning. Sometimes our keys do end up being in the kitchen, not in the hallway like we thought. Wherever we go, things happen regardless of what we believe. There doesnt appear to be any real evidence of things occurring just because we wished really hard that they would. If it did, the world would be chaotic and unpredictable because everyone would be wishing for different things.
The issue of prediction is important, and it is for that reason that scientific research assumes the existence of objective, independent truths. In science, determining the validity of a theory is accomplished through making predictions and then devising tests to see if those predictions come true. If they do, then the theory gains support; but if they dont, then the theory now has evidence against it.
This process depends upon the principles that the tests will either succeed or fail regardless of what the researchers believe. Assuming that the tests are designed and conducted properly, it doesnt matter how many of those involved believe that it will work there is always the possibility that it will instead fail. If this possibility didnt exist, then there simply wouldnt be any point in conducting the tests, would there? Whatever people came up with would be true and that would be the end of it.
Obviously that is utter nonsense. The world does not and cannot function like that if it did, we wouldnt be able to function in it. Everything we do relies upon the idea that there are things which are true objectively and independently of us therefore, truth must in fact be objective. Right?
Even if there are some some very good logical and pragmatic reasons for assuming that truth is objective, is that enough to say that we know that truth is objective? It may be if you are a pragmatist, but not everyone is. So we must inquire as to whether our conclusions here are really valid after all and, it seems, there are some reasons for doubt. These reasons gave rise to the philosophy of Skepticism in ancient Greek. More a philosophical perspective than school of thought, it continues to have a major impact upon philosophy today.