Generative AI is a kind of artificial intelligence that creates new content, including text, images, audio, and video, based on patterns it has learned from existing content. Today’s generative AI models have been trained on enormous volumes of data using deep learning, or deep neural networks, and they can carry on conversations, answer questions, write stories, produce source code, and create images and videos of any description, all based on brief text inputs or “prompts.”

Generative AI is called generative because the AI creates something that didn’t previously exist. That’s what makes it different from discriminative AI, which draws distinctions between different kinds of input. To say it differently, discriminative AI tries to answer a question like “Is this image a drawing of a rabbit or a lion?” whereas generative AI responds to prompts like “Draw me a picture of a lion and a rabbit sitting next to each other.”

This article introduces you to generative AI and its uses with popular models like ChatGPT and DALL-E. We’ll also consider the limitations of the technology, including why “too many fingers” has become a dead giveaway for artificially generated art.

Generative AI has been around for years, arguably since ELIZA, a chatbot that simulates talking to a therapist, was developed at MIT in 1966. But years of work on AI and machine learning have recently come to fruition with the release of new generative AI systems. You’ve almost certainly heard about ChatGPT, a text-based AI chatbot that produces remarkably human-like prose. DALL-E and Stable Diffusion have also drawn attention for their ability to create vibrant and realistic images based on text prompts.

Output from these systems is so uncanny that it has many people asking philosophical questions about the nature of consciousness—and worrying about the economic impact of generative AI on human jobs. But while all of these artificial intelligence creations are undeniably big news, there is arguably less going on beneath the surface than some may assume. We’ll get to some of those big-picture questions in a moment. First, let’s look at what’s going on under the hood.

Generative AI uses machine learning to process a huge amount of visual or textual data, much of which is scraped from the internet, and then determines what things are most likely to appear near other things. Much of the programming work of generative AI goes into creating algorithms that can distinguish the “things” of interest to the AI’s creators—words and sentences in the case of chatbots like ChatGPT, or visual elements for DALL-E. But fundamentally, generative AI creates its output by assessing an enormous corpus of data, then responding to prompts with something that falls within the realm of probability as determined by that corpus.

Autocomplete—when your cell phone or Gmail suggests what the remainder of the word or sentence you’re typing might be—is a low-level form of generative AI. ChatGPT and DALL-E just take the idea to significantly more advanced heights.

ChatGPT and DALL-E are interfaces to underlying AI functionality that is known in AI terms as a model. An AI model is a mathematical representation—implemented as an algorithm, or practice—that generates new data that will (hopefully) resemble a set of data you already have on hand. You’ll sometimes see ChatGPT and DALL-E themselves referred to as models; strictly speaking this is incorrect, as ChatGPT is a chatbot that gives users access to several different versions of the underlying GPT model. But in practice, these interfaces are how most people will interact with the models, so don’t be surprised to see the terms used interchangeably.

AI developers assemble a corpus of data of the type that they want their models to generate. This corpus is known as the model’s training set, and the process of developing the model is called training. The GPT models, for instance, were trained on a huge corpus of text scraped from the internet, and the result is that you can feed it natural language queries and it will respond in idiomatic English (or any number of other languages, depending on the input).

AI models treat different characteristics of the data in their training sets as vectors—mathematical structures made up of multiple numbers. Much of the secret sauce underlying these models is their ability to translate real-world information into vectors in a meaningful way, and to determine which vectors are similar to one another in a way that will allow the model to generate output that is similar to, but not identical to, its training set.

There are a number of different types of AI models out there, but keep in mind that the various categories are not necessarily mutually exclusive. Some models can fit into more than one category.

Probably the AI model type receiving the most public attention today is the large language models, or LLMs. LLMs are based on the concept of a transformer, first introduced in “Attention Is All You Need,” a 2017 paper from Google researchers. A transformer derives meaning from long sequences of text to understand how different words or semantic components might be related to one another, then determines how likely they are to occur in proximity to one another. The GPT models are LLMs, and the T stands for transformer. These transformers are run unsupervised on a vast corpus of natural language text in a process called pretraining (that’s the P in GPT), before being fine-tuned by human beings interacting with the model.

Diffusion is commonly used in generative AI models that produce images or video. In the diffusion process, the model adds noise—randomness, basically—to an image, then slowly removes it iteratively, all the while checking against its training set to attempt to match semantically similar images. Diffusion is at the core of AI models that perform text-to-image magic like Stable Diffusion and DALL-E.

A generative adversarial network, or GAN, is based on a type of reinforcement learning, in which two algorithms compete against one another. One generates text or images based on probabilities derived from a big data set. The other—a discriminative AI—assesses whether that output is real or AI-generated. The generative AI repeatedly tries to “trick” the discriminative AI, automatically adapting to favor outcomes that are successful. Once the generative AI consistently “wins” this competition, the discriminative AI gets fine-tuned by humans and the process begins anew.

One of the most important things to keep in mind here is that, while there is human intervention in the training process, most of the learning and adapting happens automatically. Many, many iterations are required to get the models to the point where they produce interesting results, so automation is essential. The process is quite computationally intensive, and much of the recent explosion in AI capabilities has been driven by advances in GPU computing power and techniques for implementing parallel processing on these chips.

The mathematics and coding that go into creating and training generative AI models are quite complex, and well beyond the scope of this article. But if you interact with the models that are the end result of this process, the experience can be decidedly uncanny. You can get DALL-E to produce things that look like real works of art. You can have conversations with ChatGPT that feel like a conversation with another human. Have researchers truly created a thinking machine?

Chris Phipps, a former IBM natural language processing lead who worked on Watson AI products, says no. He describes ChatGPT as a “very good prediction machine.”

Phipps, who’s also a comedy performer, draws a comparison to a common improv game called Mind Meld.

Certain prompts that we can give to these AI models will make Phipps’ point fairly evident. For instance, consider the riddle “What weighs more, a pound of lead or a pound of feathers?” The answer, of course, is that they weigh the same (one pound), even though our instinct or common sense might tell us that the feathers are lighter.

ChatGPT will answer this riddle correctly, and you might assume it does so because it is a coldly logical computer that doesn’t have any “common sense” to trip it up. But that’s not what’s going on under the hood. ChatGPT isn’t logically reasoning out the answer; it’s just generating output based on its predictions of what should follow a question about a pound of feathers and a pound of lead. Since its training set includes a bunch of text explaining the riddle, it assembles a version of that correct answer.

However, if you ask ChatGPT whether two pounds of feathers are heavier than a pound of lead, it will confidently tell you they weigh the same amount, because that’s still the most likely output to a prompt about feathers and lead, based on its training set. It can be fun to tell the AI that it’s wrong and watch it flounder in response; I got it to apologize to me for its mistake and then suggest that two pounds of feathers weigh four times as much as a pound of lead.