What is the difference between Jehovah's Witnesses and Pentecostals? What are the dogmatic differences between Jehovah's Witness Churches and Pentecostal Churches? Until recently I thought both churches were one and the same in beliefs.
The short version is that they are not related at all. In fact, in many major ways they are quite opposite to each other.


The Jehovah Witnesses are a "reconstructionist" sect that began in the late 1800's. They do claim to be Christian, but the reason I use the label reconstructionist sect is that they believe they are the only true Christian church, and that the rest of Christianity has become corrupt. Their organization is not based on historical Christianity but on new revelation through their prophetic publications, which have in turn guided them in the creation of a special translation of Scripture fixing what they claim to be the issues with other translations.
Pentecostalism, on the other hand, is known as a "renewal" movement. Although they have many doctrines that are distinct from the rest of Christianity, they don't claim that the rest of Christianity is totally devoid of truth. Rather than starting from scratch, they only seek to revise things a bit. Although it is a fairly new movement, dating from just the early 1900's, it has grown and taken many different shapes. Not being centrally organized, it's harder to pin any specific doctrines to Pentecostalism (as it is easy to do with the JWs because their beliefs are so precise and centrally dictated). They use the same Bible translations as other Protestants but certainly have a unique spin on some aspects of it.


There are some similarities in the early roots of Pentecostalism. One of several main roots of the movement can be traced through the Foursquare Church. Although that particular church has since taken a bit more moderate approach, its beginnings are tied up in the affairs of one Aimee Semple McPherson and her teachings, "healing ministry," and other extensive influence. Because it has many roots, and later many branches, the Pentecostal movement is not as organized or definable as a sect, but it does have some characteristic teachings such as an emphasis on continued revelation, spiritual gifts, miraculous healings, and so on.

On the other hand, the JW doctrine tends to be much more concrete. They believe in various specific end times predictions (some of which have morphed as dates come and go), and are very precise about things like terms of service to the church, doing good deeds, and so on.

In summary, while they both began at roughly the same time and some parallels could be drawn in the way they first started, they are completely different entities. Early on they were driven by very different influences, and they have become very different beasts. Their teachings bear little resemblance to each other, and many of their teachings are mutually exclusive.