I've read some books from behavioral economy to emotional intelligence, and it kind of makes sense, but when it comes to psychology it feels to me a bit like astrology, where there are some things that can work, but mostly because of auto-suggestion, or any other kind of suggestions, and things like the placebo (or even the nocebo) effect. So, I wonder if psychology is a science and why so many people rely on it.
"Science" refers to a methodology for obtaining knowledge, and often to the knowledge itself as well. Science is often confused with another term "technology", that refers to the application of such knowledge for practical uses. Some people might incorrectly refer to "computers" and "cars" as examples of "science", when in fact they are examples of "technology".
Psychology is similarly divided. The science part is called "research psychology", or just "psychology". The technology part is called "applied psychology", that includes psychotherapy, and I think that's what this question is really about.
Clinical psychology is not technically a science, but an applied science, or in other words, a technology. If you are wondering how science-based different schools of psychotherapy are, then check out this related question: Which schools of psychotherapy are most credible to a hard scientist?. If you've seen a psychoanalyst recently for example, and you think it's kinda hoaky, well then, you're probably right - psychoanalysis is not generally considered to be science-based, and is comparable to astrology (pseudoscience) in that sense.
On the other hand, other schools of psychotherapy have a more scientific basis: Cognitive-behavioural therapy has been shown to be efficacious (above placebo) for a wide variety of common disorders, and behavioural therapy bases all its techniques directly on scientific findings.
when it comes to psychology it feels to me a bit like astrology, where there are some things that can work, but mostly because of auto-suggestion, or any other kind of suggestions, and things like the placebo (or even the nocebo) effect. So, I wonder if psychology is a science and why so many people rely on it.
A key point is that your question seems to be leaving out is that psychology is not only about treating mental problems--it is also about understanding the mind. It addresses scientific questions like:
- How do children acquire language?
- What is the effect of others' actions on our own actions?
- Is intelligence one "thing", or are there multiple intelligences?
- What are the most common traits of personality?
- How do we develop our morals and/or ethics?
- How do most people make decisions?
- What is the effect of viewed violence on episodic memory?
- and so many more...
Modern psychology, in addressing these sorts of questions, is a science. It uses research methods like random assignment; experimental and control groups; establishing baselines; manipulating independent variables and measuring dependent variables; eliminating confounds; testing hypotheses, using statistics (heavily!); interacting with other disciplines, like neuroscience, anthropology, ethology, or sociology; publishing peer-reviewed papers, revising faulty models; etc.
And then, even when, in applied psychology, the intention is to treat mental disorders, scientific approaches are used. Treatment groups are compared with control groups, case studies are published, patients can be followed for years, behavior is measured and quantified, statistics are run, etc.
Taking a good Psychology 101/General Psychology course should make this point a thousand times over. Modern psychology should not feel anything like astrology.
As an Industrial/Organizational Psychologist practicing Human Factors in a large organization, I use scientific method to inform product and service design. Our dependent variables (effectiveness, efficiency, satisfaction, enjoyment, coolness) are measured across controlled experimental conditions. We practice stronger science than most physical scientists due to the amount of covariates in human behavior.
In answering this question as stated, one should consider the 56 different types of psychology defined by the divisions of the American Psychological Association (http://www.apa.org/about/division/).
Additionally, Wikipedia (https://en.wikipedia.org/wiki/Psychology) states that "Psychologists employ empirical methods to infer causal and correlational relationships between psychosocial variables." This is a scientific method.
Just to pick up on the following comment: "where there are some things that can work, but mostly because of auto-suggestion, or any other kind of suggestions, and things like the placebo (or even the nocebo) effect."
The examples you have (auto-suggestion and emotional intelligence) suggest that you've been reading "pop-psychology" books which aim to sell ideas rather than promote good science. From reading into your question, i'm guessing that its about whether psychology is actually any better at describing, explaining and predicting behaviour, when compared to a field which does this by questionable means (e.g. astrology).
The examples you picked represent fairly niche, small areas of psychology (auto-suggestion really just seems to be a pseudo-psychology buzz word not really coming from academics but business/self-help moguls).
Clearly, you can pick areas of psychology where we have been unable to correctly predict behaviour. A recent example comes from a big project on seeing how well psychology studies can be replicated (https://www.sciencemag.org/content/349/6251/aac4716.abstract) showing that the majority of published studies could not be replicated by a different research team (however, this issue isn't unique to psychology, and is often even worse in other "scientific" fields http://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.0020124).
On the whole though, lots of psychological theories that are more based on the scientific literature have been replicated and are able to predict behaviour in a variety of different contexts. Clearly using psychological theory doesn't mean you can have complete control of other people's behaviour, and often changing behaviour can be difficult. I would agree that many people rely on pseudo-scientific "psychological" theories that have been over-sold by people who want to make money, whether its through being a consultant or to just sell books. If you want a good example of how social psychology has been applied to benefit society, then i'd pick up a new book from the government's psychology unit (http://www.eburypublishing.co.uk/editions/insightful-thinking/9780753551387). There are also countless exmaples of how psychology has been better able to make us understand and treat a variety of different disorders too!
Let me first rewrite "the argument" you may find attractive/puzzling:
$Premise$ 1: behavioral economy to emotional intelligence makes sense (implying that they are "science").
$Premise$ 2: if there are auto-suggestion, or any other kind of suggestions, e.g.,placebo effect (for some thing in psychology), then some thing can work in psychology (implying some other things may not work).
$Conclusion$: Psychology does not seem to be "science", and people who rely on it seems less than sensible.
I would like to point out,
From $Premise$ 1, it seems that the way you define "science" is what "makes sense," or the way I interpret your expressed opinion is that "science" is what is intuitively convincing for (intelligible) people (e.g., yourself).
From $Premise$ 2, your expressed opinions seem to be puzzling, I am not sure what you meant by "suggestion" and "auto-suggestion." But from the example you provided, i.e., placebo effect, I conjecture that you are trying to say that psychology of some sort has pragmatic value because "suggestion" influences people. And what you may have meant but may have not expressed may be that "suggestion" seems to possess pragmatic values solely because "suggestion" $just$ influences people, and for a person as intelligible as yourself find this brute fact (that is, things like "suggestion") rather unsatisfying to study since it does not seem to lead to any pragmatic normative or empirical investigations.
Thus, you reached your puzzle, since psychology is of less pragmatic values, and less intuitively convincing, how can it be science?
I would like to note that, the term "science" can refer to different things, the meaning of this term changes throughout the history. I have not carefully read the whole page, but wikipedia seems to have some information that may help illustrate my point: https://en.wikipedia.org/wiki/Science
I would like to note that, "science" originates from the noun of the latin verb, $scire$ $(know)$. Thus, I derive that science is simply knowledge. To add on that, since that you seem to expect "knowledge" to be somewhat "empirically true," that is, to some extent, this knowledge must refer to or shed lights on how nature (including human mind) works, or how nature seems to and will be expected to work from our (future) experiences. I arrived at this notion because you credit "astrology," which seems accidental and does not conform to our experiences, as non-science.
You must have found my answer tedious and unsatisfying so far since I have only provided some clarification on possible interpretations of your question, but not an answer of why psychology is science or is psychology science.
Modern psychology seems to be empirical in nature, that is, modern psychology, to my knowledge, seems to either derived based on experiences (e.g., experiments to data to psychology theories) or developed to serve empirical investigations (e.g., theoretical psychology construed to serve as the foundation or hypothesis in empirical experiments). I would encourage you to take some look at APA approved journals or psychology articles on PubMed. I would not like you to make up your mind about psychology solely based on pop psychology books or articles for general public that are less than rigorous. Those empirical articles are quite convincing intuitively to intelligible readers like yourself. The theoretical ones, though not immediately intuitive, may make sense if you are willing to read the works this or that theory is based on and empirical articles associated with those theories.
A few things to point out based on the answer provided by the answer @Arnon Weinberg:
your note on "science" and "technology" seems a bit puzzling (because your explanation on "science" though seems to be correct to some extent, your explanation on "technology" seems less than convincing) and does not seem to be necessary. Your example with "computer" for example, I would call it neither "technology" nor "knowledge." At best, maybe "theoretical computer science" is "science" and "computer science technique" is "technology" based on your definition.
Your way of dividing psychology based on your "technology" and "science" division seems puzzling. "clinical psychology" can be "science" even from your point of view, e.g., studies pertaining to catastrophizing influences chronic pain patient's quality of life are simply using scientific method to derive knowledge that may be of applicable value but they are not applications of knowledge.
your answer suddenly sabotages your own question by suggesting that what you were interested was on psychotherapy, by which, I conjecture, you mean that you real question is "is psychotherapy scientific?" This question is fine and your latter part captures this question well except that you confuse applied science with technology. By your own word, technology is the application of the science. Applied science, to my knowledge, is science that concerns application, or science of applicable value, which is $technically$ science. For example, applied math may study the normal equation to solve for the best least square solution, normal equation here is applied science. The technology, by your definition, can be a software built on normal equation, which is an application of the normal equation.
Another note on psychoanalysis: psychoanalytic theories nowadays are often studied by philosophy and/or history and are less received in psychology since it does not seem to be evident-based. However, there are some psychologists of psychoanalytic inclination actively conducting empirical experiments to either modify or validate $modern$ psychoanalytic theories (which is way more developed and refined than Fraud's). Also, CBT or the cognitivism and behaviorism behind other traditions of psychotherapy approach often utilizes psychoanalytic's ideas. For example, a psychotherapist of any theoretical orientation may borrow some modern psychoanalytic theories for case conception.
One final point, I think this question, though pertaining to cognitive science, may be better received in the philosophy forum since it seems to be relevant to philosophy of science and philosophy of psychology.