“If no practical difference whatever can be traced, then the alternatives mean practically the same thing, and all dispute is idle.” William James 
The Stanford Encyclopedia of Philosophy (SEP) article, “Causal Determinism”, describes determinism in several different ways. Some of these are good. Some are not.
“The roots of the notion of determinism surely lie in a very common philosophical idea: the idea that everything can, in principle, be explained, or that everything that is, has a sufficient reason for being and being as it is, and not otherwise.”  (SEP)
Determinism is based in the belief that the physical objects and forces that make up our universe behave in a rational and reliable fashion. By “rational” we mean that there is always an answer to the question, “Why did this happen?”, even if we never discover that answer.
This belief gives us hope that we may uncover the causes of significant events that affect our lives, and, by understanding their causes, gain some control over them. Medical discoveries lead to the prevention and treatment of disease, agricultural advancements improve our world’s food supply, new modes of transportation expand our travel, even to the moon and back, and so forth for all the rest of our science and innovation. Everything rests upon a foundation of reliable causation.
“Causal determinism is, roughly speaking, the idea that every event is necessitated by antecedent events and conditions together with the laws of nature.”  (SEP)
A logical corollary of reliable causation is causal necessity. Each cause may be viewed as an event, or prior state, that is brought about by its own causes. Each of these causes will in turn have their own causes, and so on, ad infinitum. Thus, reliable causation implies the logical fact that everything that happens is “causally necessary”. Everything that has happened, or will happen, will only turn out one way. A key issue in determinism is what to make of this logical fact.
Determinism itself is neither an object nor a force. It cannot do anything. It does not control anything. It is not in any way an actor in the real world. It is only a comment, an assertion that the behavior of objects and forces will, by their naturally occurring interactions, bring about all future events in a reliable fashion.
So, the next step is to understand the behavior of the actual objects and forces.
“Determinism is deeply connected with our understanding of the physical sciences and their explanatory ambitions…”  (SEP)
We observe that material objects behave differently according to their level of organization as follows:
(1) Inanimate objects behave passively, responding to physical forces so reliably that it is as if they were following “unbreakable laws of Nature”. These natural laws are described by the physical sciences, like Physics and Chemistry. A ball on a slope will always roll downhill. Its behavior is governed by the force of gravity.
(2) Living organisms are animated by a biological drive to survive, thrive, and reproduce. They behave purposefully according to natural laws described by the life sciences: Biology, Genetics, Physiology, and so on. A squirrel on a slope will either go uphill or downhill depending upon where he expects to find the next acorn. While still affected by gravity, the squirrel is no longer governed by it. It is governed instead by its own biological drives.
(3) Intelligent species have evolved a neurology capable of imagination, evaluation, and choosing. They can behave deliberately, by calculation and by choice, according to natural laws described by the social sciences, like Psychology and Sociology, as well as the social laws that they create for themselves. While still affected by gravity and biological drives, an intelligent species is no longer governed by them, but is instead governed by its own choices.
So, we have three unique causal mechanisms, that each operate in a different way, by their own set of rules. We may even speculate that quantum events, with their own unique organization of matter into a variety of quarks, operates by its own unique set of rules.
A naïve Physics professor may suggest that, “Everything can be explained by the laws of physics”. But it can’t. A science discovers its natural laws by observation, and Physics does not observe living organisms, much less intelligent species.
Physics, for example, cannot explain why a car stops at a red traffic light. This is because the laws governing that event are created by society. While the red light is physical, and the foot pressing the brake pedal is physical, between these two physical events we find the biological need for survival and the calculation that the best way to survive is to stop at the light.
It is impossible to explain this event without addressing the purpose and the reasoning of the living object that is driving the car. This requires nothing that is supernatural. Both purpose and intelligence are processes running on the physical platform of the body’s neurology. But it is the process, not the platform, that causally determines what happens next.
We must conclude then, that any version of determinism that excludes purpose or reason as causes, would be invalid. There is no way to explain the behavior of intelligent species without taking purpose and reason into account.
Finding Ourselves in the “Causal Chain”
So where do we find ourselves in this deterministic universe? We are physical objects, living organisms, and an intelligent species. As such we are capable of physical, purposeful, and deliberate causation. We can imagine different methods to achieve a goal, estimate their likely outcomes, and then choose what we will do. When we act upon this chosen will, we are forces of nature. We clear forests, build cities and cars, and even raise the temperature of the planet.
But determinism, unlike us, is neither an object nor a force. It is simply the belief that our behavior can be fully explained, in terms of some specific combination of physical, biological, and rational causation.
We must conclude, then, that any version of determinism that bypasses or excludes human causal agency, in cases where it is clearly involved, would be invalid.
By convention, we call the result, of the mental process of choosing what we will do, a “freely chosen will”, or simply “free will”. The word “free” means that the choice was our own, as opposed to a one imposed upon us by external coercion or some other undue influence.
In all cases of a freely chosen will, two facts are simultaneously true:
(A) We have made our choice according to our own purpose and our own reasons, therefore it was made of our own free will.
(B) We have made our choice according to our own purpose and our own reasons, therefore it was causally determined.
Okay, now that we find free will and determinism to be logically compatible, let’s see how can we mess this up …
Error, By Tradition
“Determinism: The world is governed by (or is under the sway of) determinism if and only if, given a specified way things are at a time t, the way things go thereafter is fixed as a matter of natural law.”  (SEP)
In this formal definition from the SEP article, we now have determinism anthropomorphically appearing as an actor in the real world. And not just any actor, but one with the power to “govern” everything that happens. Even less attractive is the suggestion that it might also be viewed as a Svengali, holding everything “under its sway”.
In either case, we are given the impression that our destiny is no longer chosen by us, but is controlled by some power that is external to us. And that viewpoint is functionally equivalent to this:
“Fatalism is the thesis that all events (or in some versions, at least some events) are destined to occur no matter what we do. The source of the guarantee that those events will happen is located in the will of the gods, or their divine foreknowledge, or some intrinsic teleological aspect of the universe…”  (SEP)
The SEP article attempts to draw a distinction between determinism and fatalism, by attributing the external control in determinism to “natural law” rather than “the will of the gods”. But as long as the cause remains a force that is external to us, it is only “a distinction without a difference”.
Delusion, By Metaphor
The SEP article seems to be aware of the metaphorical nature of their definition:
“In the loose statement of determinism we are working from, metaphors such as ‘govern’ and ‘under the sway of’ are used to indicate the strong force being attributed to the laws of nature.”  (SEP)
“In the physical sciences, the assumption that there are fundamental, exceptionless laws of nature, and that they have some strong sort of modal force, usually goes unquestioned. Indeed, talk of laws ‘governing’ and so on is so commonplace that it takes an effort of will to see it as metaphorical.”  (SEP)
Take a moment to appreciate the irony. It “takes an effort of will” to see it for what it is.
It is the fashion these days to refer to free will as an “illusion” while imparting causal powers to determinism. But, in the real world, the opposite is true. Determinism, being neither an object nor a force, causes nothing in the real world. However, the object we call a “human being”, estimates the best choice and acts upon it, physically bringing about the future, in a causally reliable way.
The process of making a decision is not an illusion. It is an empirical event. A neuroscientist, performing a functional MRI while someone is making a decision, can point to the activity monitor, and say, “Look, there, he’s doing it right now.” So, there is no “illusion” as to who is doing what, and where causal agency resides. And it will also be an empirical fact as to whether a person made the decision for themselves, or whether the choice was imposed upon him by someone else, against his will, either through coercion or some other undue influence.
The view that determinism is an object or a force of nature, acting to bring about events in the real world, is a delusion we create when we take the metaphorical expressions literally.
Dealing with the Inevitable
“In a looser sense, however, it is true that under the assumption of determinism, one might say that given the way things have gone in the past, all future events that will in fact happen are already destined to occur.”  (SEP)
“… the existence of the strings of physical necessity, linked to far-past states of the world and determining our current every move, is what alarms us.”  (SEP)
So, what should we make of the logical fact of causal inevitability?
Not much, really. All the benefits of reliable cause and effect come from knowing the specific causes of specific effects. The single fact that everything that happens is always causally inevitable tells us nothing useful. It cannot help us to make any decision, because all it can tell us is that whatever we decide, it will be inevitable. It is like a constant that always appears on both sides of every equation, and can be subtracted from both sides without affecting the result.
The SEP error here is the suggestion that a prior point in time is sufficient to cause a future event. That is incorrect. No event will occur until all its prior causes have played out.
For example, a woman decides to build a playground in the backyard for her kids. She draws up the plans, buys the materials, spends hours sawing, drilling, putting it together, and painting it. The playground, now in her backyard, is the inevitable result of prior events, specifically, her decision, her planning, her purchasing, and her labor.
In theory, we could trace back, through an ever-widening network of prior causes, to explain how the woman happened to be there, on the planet Earth, at the time she decided to build the playground. But the farther we move away from the current event, the less relevant and more coincidental each prior cause becomes.
The most meaningful and relevant cause of the playground was her love for her children. And that did not exist anywhere else in the universe prior to her.
Therefore, we cannot attribute the cause of the playground to, say, the Big Bang. There was nothing about the Big Bang that “already caused”, “already destined”, “already fixed”, or “already determined” that there would be a playground in that backyard.
We may say that it was inevitable, from any prior point in eternity, that a playground would show up in her backyard. But we cannot truthfully assert that it was “caused” by that prior point. An event is never caused until it is completely caused. It cannot be “pre-caused”. And it never would have happened except for the desire of the woman to bring it about.
When we choose what we will do, and act upon that choice, we are the final responsible cause of the inevitable result. And while our choice was itself inevitable, it was never anything other than our own choice.
Yes, I Could Have Done Otherwise (the Semantics of Possibilities)
Deterministic inevitability is about what will happen in the real world. But this in no way restricts what can and cannot happen. The inevitable and the possible exist in separate semantic contexts.
When speaking of what we can and cannot do, our context is the mental process of imagination. We use our imagination to play out possible futures, to estimate what might happen if we choose this option rather than that option.
We can have as many possibilities as we can imagine. If we foresee an insurmountable roadblock for one possibility, then we may discard it as an “impossibility”. If a possibility is not feasible to implement, then we say it is not a “real” possibility. But all possibilities that could be implemented, if chosen, are referred to as real possibilities.
The possibility that we implement becomes the inevitable actuality. Our choice is the inevitable result of our purpose and our reasons. Our purpose and our reasons are the inevitable result of who we are at that moment. Who we are at that moment, is the inevitable result of our interactions with our physical and social environment up to that point, including all the other choices we made along the way. We are active participants in causally determining who we become.
So, we begin with multiple possibilities, and from them we choose what will become the single inevitable actuality.
Now, if things don’t turn out as we imagined they would, then we may reconsider our choice, and consider what we could have done otherwise. This mental process of reconsideration is how we learn from our mistakes, and how we adjust our future choices to produce better outcomes.
If we had more than one real possibility, then it is always true that we could have done otherwise. But, it is also always true that we wouldn’t have done otherwise, at that unique point in time. If we have a choice between A and B, then at that time “we can choose A” and “we can choose B” are each true. And at the end, it is also true that “I chose A, but I could have chosen B instead.” That’s how the notion of “can” operates. It lives in the context of a future that is imagined, but that might never be actualized.
In summary, what we can do is different from what we will do. When the two are wrongly conflated, we end up with a semantic falsehood, such as “I could not have done otherwise”, when what we intend to say is that “I would not have done otherwise”.
Within the domain of human influence (things we can do something about), the single inevitable actuality is often the result of considering multiple possibilities, and choosing the one we wish to implement. In a deterministic causal chain the multiple possibilities are just as inevitable as the single actuality. They are unavoidable.
Much Ado About Nothing
Determinism asserts that everything that happens is always causally inevitable. But, as we’ve seen above, this is not an inevitability that is “beyond our control”, but rather an inevitability that incorporates our choices and our control in the overall scheme of causation.
We are not “puppets” of any external force that is “pulling our strings”. We are physical, living, intelligent beings that exercise considerable control over our environment.
The fact that everything that happens is always causally inevitable is nothing we need to fear. What we will inevitably do is exactly identical to us just being us, doing what we do, and choosing what we choose. Thus, causal inevitability is not a meaningful constraint. It is not something that we can or need to be “free of”.
The logical fact of causal inevitability is not a meaningful or relevant fact. All the utility of reliable causation comes from knowing the specific causes of specific effects. But the single fact of causal inevitability only can tell us that whatever happens will have been inevitable. The reasonable mind simply acknowledges it, and then forgets it.
Why We Need to Get This Right
(1) It is good to know the truth. The truth is that determinism does not cause objects to behave reliably. Objects and forces are already behaving in a rational and reliable fashion, and determinism simply takes note of this fact. We observe the Earth reliably circling the Sun every 365.25 days. We observe people reliably steering their cars away from the edge of a cliff, rather than driving off it. Determinism asserts that both events are reliably explained by some combination of physical, biological, or rational causal mechanism.
(2) We need to be able to speak coherently about determinism and freedom. We do not find coherence in these statements from Albert Einstein during an interview in 1929:
“In a sense, we can hold no one responsible. I am a determinist. As such, I do not believe in free will. … Practically, I am, nevertheless, compelled to act as if freedom of the will existed. If I wish to live in a civilized community, I must act as if man is a responsible being.” 
Why suggest that he must believe in something that he claims is untrue? In truth, free will is when we choose for ourselves what we will do, when free from external coercion or other undue influence. This is not a question of belief, but a question of empirical fact. Either we made the decision, or someone (coercion) or something else (mental illness) imposed the choice upon us.
(3) “Free will” never has, nor ever could mean “freedom from causation”. There is no freedom without reliable cause and effect. The SEP notes that David Hume made this point:
“Hume went so far as to argue that determinism is a necessary condition for freedom—or at least, he argued that some causality principle along the lines of ‘same cause, same effect’ is required.”  (SEP)
To put it succinctly, “freedom from reliable causation” is an oxymoron. Without reliable cause and effect, we could not reliably cause any effect, and would have no freedom to do anything at all.
(4) In matters of justice, in the context of moral and legal responsibility, there is a reasonable “no free will” exception. When someone is forced against their will to participate in a crime, we assign responsibility for his actions to the person holding the gun to his head. But when a crime is the result of a deliberate decision to profit at the expense of someone else, then we must address that cause through correction and rehabilitation. The suggestion that no one is ever responsible for anything, because no one has free will, is both empirically false and morally corrupting.
(5) We are psychologically battered by the “hard” determinist’s nihilistic ramblings about people having no control over their lives, being merely “puppets on a string”, just another “falling domino”, or a “passenger on a bus” being driven by a fate over which they have no control. The reality is that people begin actively negotiating their destiny as soon as they are born. Ask any parent awakened at 2AM by their newborn infant’s cries to be fed. Or observe the toddler learning to walk, both accommodating and overcoming the force of gravity.
(6) Our freedom is not threatened by determinism, because determinism is not an external force acting upon us. Determinism is simply us being us, doing what we do, and choosing what we choose. That is not a meaningful constraint. Thus, we have no need to escape via supernaturalism, chaos, randomness, or quantum indeterminism. Philosophy can leave theology to the theists, physics to the physicists, and perhaps assist them when they get tangled in their semantics.
 James, William. Pragmatism (Dover Thrift Editions) (p. 16). Dover Publications. Kindle Edition.
 Hoefer, Carl, “Causal Determinism”, The Stanford Encyclopedia of Philosophy (Spring 2016 Edition), Edward N. Zalta (ed.), https://plato.stanford.edu/archives/spr2016/entries/determinism-causal/
 “The Saturday Evening Post”, Oct 26, 1929, “What Life Means to Einstein”, An Interview By George Sylvester Viereck. Link:
 Hoefer, Carl, … (SEP)