A robust epistemology is a sufficient condition for a successful pursuit of scientific inquiry. There are many other factors and conditions that must be met for science but a vigorous epistemic model for how one pursues scientific inquiry is needed; otherwise, there may be sufficient reasons to doubt not only the conclusions of the scientific inquiry but as well as the pool of data, which must be assessed appropriately. The scientist is more than welcome to pursue an empiricist model for his epistemology, though strict [naturalistic] empiricism is not very robust, but it must have certain allowances for metaphysical import—perhaps more rationalistic.
I believe the best way to construct a robust epistemology and scientific method is to be a realist. What I mean by this is that the external reality is how it appears to be to an observer making an epistemic inquiry, the measurements from science accurately depicts reality. This is in contrast to instrumentalism/anti-realism, which suggests that our inquiry of the world, scientifically, do not accurately depict reality but as useful fictions. An instrumentalist is more concerned about data fitting theories and predictions than with an accurate depiction of reality.
For the scientific realist, the ontology of the world determines one’s epistemology. They congruently correspond. It is important to note the order of entailment. Antecedently, reality determines our epistemology. It would be illicit to reverse the term order would be an epistemic fallacy. I am not advocating a naïve realism where reality acts on the human mind without personal inquiry nor am I advocating postmodern anti-realism where one can construct whatever type of reality is desired. I am advocating a form of critical realism (or critical non-realism in certain instances concerning theoretical entities when there may be reason to suspect insufficient knowledge of the theoretical entity).
The first issue concerning an empiricist epistemology would be the issue of justification. The justification of our beliefs in propositions describing physical objects is always inferential and that it is always from propositions about the nature of our experiences that such inferences are made. With this said, there are two conditions that must be satisfied concerning inferential belief in physical objects: 1) Statements about experience must count as reasons or evidence for statements about objects and 2) Statements about experience must in some, no doubt rather obscure, sense be accepted by those who make statements about objects. However, in order to ground these beliefs one must always be in the appropriate phenomenological frame of mind. All conditions for a right phenomenological state of mind aside, one must account for inferential beliefs. Some beliefs are inferentially justified but are not usually if ever consciously inferred from that which would constitute evidence, which would be beliefs about the future or subjunctive conditionals. The belief that this glass of water in front of me will quench my thirst if I drink it is not inferred back from previous experiences coupled with an application of a synthetic a priori principle of induction. Though this example is not how we form our beliefs psychologically or historically, it can be formed via instances of past experience and induction in the logical sense.
For the rest of the article see the second part soon to come.
 R.A. Fumerton, “Inferential Justification and Empiricism.” The Journal of Philosophy 73 (1976): 559-60.