Now it is possible that you think science and religion can fill those roles and are better choices as they have more defined processes to follow. But further deliberation undermines those alternatives. Starting with science, it is difficult to imagine anyone in today’s world not considering science in thinking about philosophical issues. I want to make clear that I believe that science offers the most definitive answers to questions about the nature of physical reality and science-driven technology clearly is the best means to solve most everyday problems and enhance our daily life. Science is also incredibly useful in arguing many points in philosophy, such as the nature of the mind.
However it seems to me science breaks down when trying to answer larger questions such as those posed by ethics (right versus wrong actions) and metaphysics (e.g. free will). Science struggles with being molded to answer a question such as whether there is a God. It cannot easily answer questions about happiness, justice, beauty, or even love and friendship. It is best at telling us how the material world works, but is often not designed to answer many questions about why things are as they are. Psychology, to suggest a specific scientific field, can give us fascinating insights into human behavior, but is less well equipped to show us the means to contentment, self-worth, and human meaning.
On the other hand religion appears to be useful to many people, and I do not wish to detract or even argue against personal beliefs. However religion is based on faith which appears to be unevenly distributed among people and is of variable intensity even among its proponents. Religious experiences are so individualized that they appear unreliable or illusory. Religious dogma is strongly dependent on revelation which may be inaccurately or even untruthfully recorded throughout history. Spiritual texts are frequently enigmatic, metaphorical, and open to varying interpretations. Philosophy is useful within religion as a tool to analyze sacred documents. Moreover faith can be further strengthened by reason. At a minimum, philosophy is a tool that allows religious practitioners to develop an internally consistent understanding of their religion and faith, perhaps avoiding harms like those done in the name of religion in the past.
At the end of the day, the greatest scientists and theologians (for example Einstein and St. Augustine) have fallen back on philosophy as vital to understanding their beliefs about life, mankind, and the universe. I’ll take their word for it that philosophy has much to offer the thoughtful scientist and person of faith.