However, when we assess whether a claim is true, all we can ever do is assess whether it agrees with our understanding of the matter in question at the moment that we reach our conclusion - which means assessing whether it agrees with what we believe about the matter in question at that moment.

For example, in order to conclude that the claim ‘Tomorrow is Monday’ is true we must first believe that tomorrow is Monday - whether we formed that belief before or during our assessment. 

Are you assuming a coherence theory of truth?  It sounds like you do when you say the only way to assess whether a claim is true is to assess whether it agrees (coheres?) with what we believe about the matter in question at that moment.  Does your argument still stand if we hold other theories of Truth?  What about a correspondence theory, or a pragmatic theory of Truth?

I disagree with your example.  To conclude that the claim 'Tomorrow is Monday' is true, I do not need to first believe that tomorrow is Monday.  I need only know that Today is Sunday, and know that days follow the ordered sequence Sunday, Monday, Tuesday, ...  I can logically infer that Tomorrow is Monday is true without believing it a priori or simultaneously.  Most mathematical proofs work this way.  I do not need to believe the Riemann Hypothesis in order to conclude that the Riemann Hypothesis is true. I need only form a mathematical argument and see where it leads.


People did not first believe Newtons Laws and then conclude that they were true.  They saw that the laws predicted events accurately, saw that they were true in a correspondence or pragmatic sense, and then came to believe them.